[textinput] segmentation violation on Undo shortcut

[ferdymercury]

Describe the bug

root -l
root [0] 
 *** Break *** segmentation violation



===========================================================
There was a crash (kSigSegmentationViolation).
This is the entire stack trace of all threads:
===========================================================
#0  0x00007f0659a6f337 in __GI___waitpid (pid=9428, stat_loc=stat_loc
entry=0x7ffe370ff9b8, options=options
entry=0) at ../sysdeps/unix/sysv/linux/waitpid.c:30
#1  0x00007f06599da047 in do_system (line=<optimized out>) at ../sysdeps/posix/system.c:149
#2  0x00007f065a771a08 in TUnixSystem::Exec (this=0x55b1312be7c0, shellcmd=0x55b13202b340 "/opt/root_bld/etc/gdb-backtrace.sh 9396 1>&2") at /opt/root_src/core/unix/src/TUnixSystem.cxx:2108
#3  0x00007f065a7722b9 in TUnixSystem::StackTrace (this=0x55b1312be7c0) at /opt/root_src/core/unix/src/TUnixSystem.cxx:2399
#4  0x00007f065a775f5a in TUnixSystem::DispatchSignals (this=0x55b1312be7c0, sig=kSigSegmentationViolation) at /opt/root_src/core/unix/src/TUnixSystem.cxx:3619
#5  0x00007f065a76d70e in SigHandler (sig=kSigSegmentationViolation) at /opt/root_src/core/unix/src/TUnixSystem.cxx:395
#6  0x00007f065a775e67 in sighandler (sig=11) at /opt/root_src/core/unix/src/TUnixSystem.cxx:3590
#7  0x00007f065a76642a in textinput::TerminalConfigUnix::HandleSignal (this=0x7f065ac559a0 <textinput::TerminalConfigUnix::Get()::s>, signum=11) at /opt/root_src/core/textinput/src/textinput/TerminalConfigUnix.cpp:99
#8  0x00007f065a766146 in (anonymous namespace)::TerminalConfigUnix__handleSignal (signum=11) at /opt/root_src/core/textinput/src/textinput/TerminalConfigUnix.cpp:36
#9  <signal handler called>
#10 0x00007f065a0b8a4e in std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >::_M_assign(std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > const&) () from /usr/lib/x86_64-linux-gnu/libstdc++.so.6
#11 0x00007f065a0b8e19 in std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >::operator=(std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > const&) () from /usr/lib/x86_64-linux-gnu/libstdc++.so.6
#12 0x00007f065a75e3b1 in textinput::Text::operator= (this=0x55b13203e698) at /opt/root_src/core/textinput/src/textinput/Text.h:29
#13 0x00007f065a75d374 in textinput::Editor::ProcessCommand (this=0x55b131ae5c50, M=textinput::Editor::kCmdUndo, R=...) at /opt/root_src/core/textinput/src/textinput/Editor.cpp:386
#14 0x00007f065a75babe in textinput::Editor::Process (this=0x55b131ae5c50, cmd=..., R=...) at /opt/root_src/core/textinput/src/textinput/Editor.cpp:65
#15 0x00007f065a76bc3b in textinput::TextInput::ProcessNewInput (this=0x7f065ac55820 <(anonymous namespace)::TextInputHolder::getHolder()::sTIHolder>, in=..., R=...) at /opt/root_src/core/textinput/src/textinput/TextInput.cpp:174
#16 0x00007f065a76b8b5 in textinput::TextInput::ReadInput (this=0x7f065ac55820 <(anonymous namespace)::TextInputHolder::getHolder()::sTIHolder>) at /opt/root_src/core/textinput/src/textinput/TextInput.cpp:126
#17 0x00007f065a75a2d9 in Getlinem (mode=kOneChar, prompt=0x0) at /opt/root_src/core/textinput/src/Getline.cxx:256
#18 0x00007f065ac8f645 in TRint::HandleTermInput (this=0x55b131317310) at /opt/root_src/core/rint/src/TRint.cxx:588
#19 0x00007f065ac8d1a1 in TTermInputHandler::Notify (this=0x55b13203f9e0) at /opt/root_src/core/rint/src/TRint.cxx:132
#20 0x00007f065ac91a07 in TTermInputHandler::ReadNotify (this=0x55b13203f9e0) at /opt/root_src/core/rint/src/TRint.cxx:124
#21 0x00007f065a76fcb5 in TUnixSystem::CheckDescriptors (this=0x55b1312be7c0) at /opt/root_src/core/unix/src/TUnixSystem.cxx:1310
#22 0x00007f065a76ef2b in TUnixSystem::DispatchOneEvent (this=0x55b1312be7c0, pendingOnly=false) at /opt/root_src/core/unix/src/TUnixSystem.cxx:1065
#23 0x00007f065a654eb5 in TSystem::InnerLoop (this=0x55b1312be7c0) at /opt/root_src/core/base/src/TSystem.cxx:406
#24 0x00007f065a654c4a in TSystem::Run (this=0x55b1312be7c0) at /opt/root_src/core/base/src/TSystem.cxx:356
#25 0x00007f065a5dce87 in TApplication::Run (this=0x55b131317310, retrn=false) at /opt/root_src/core/base/src/TApplication.cxx:1607
#26 0x00007f065ac8ec5d in TRint::Run (this=0x55b131317310, retrn=false) at /opt/root_src/core/rint/src/TRint.cxx:473
#27 0x000055b1304a30fe in main (argc=1, argv=0x7ffe37104bf8) at /opt/root_src/main/src/rmain.cxx:83
===========================================================


The lines below might hint at the cause of the crash.
You may get help by asking at the ROOT forum https://root.cern/forum
Only if you are really convinced it is a bug in ROOT then please submit a
report at https://root.cern/bugs Please post the ENTIRE stack trace
from above as an attachment in addition to anything else
that might help us fixing this issue.
===========================================================
#10 0x00007f065a0b8a4e in std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >::_M_assign(std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > const&) () from /usr/lib/x86_64-linux-gnu/libstdc++.so.6
#11 0x00007f065a0b8e19 in std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >::operator=(std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > const&) () from /usr/lib/x86_64-linux-gnu/libstdc++.so.6
#12 0x00007f065a75e3b1 in textinput::Text::operator= (this=0x55b13203e698) at /opt/root_src/core/textinput/src/textinput/Text.h:29
#13 0x00007f065a75d374 in textinput::Editor::ProcessCommand (this=0x55b131ae5c50, M=textinput::Editor::kCmdUndo, R=...) at /opt/root_src/core/textinput/src/textinput/Editor.cpp:386
#14 0x00007f065a75babe in textinput::Editor::Process (this=0x55b131ae5c50, cmd=..., R=...) at /opt/root_src/core/textinput/src/textinput/Editor.cpp:65
#15 0x00007f065a76bc3b in textinput::TextInput::ProcessNewInput (this=0x7f065ac55820 <(anonymous namespace)::TextInputHolder::getHolder()::sTIHolder>, in=..., R=...) at /opt/root_src/core/textinput/src/textinput/TextInput.cpp:174
#16 0x00007f065a76b8b5 in textinput::TextInput::ReadInput (this=0x7f065ac55820 <(anonymous namespace)::TextInputHolder::getHolder()::sTIHolder>) at /opt/root_src/core/textinput/src/textinput/TextInput.cpp:126
#17 0x00007f065a75a2d9 in Getlinem (mode=kOneChar, prompt=0x0) at /opt/root_src/core/textinput/src/Getline.cxx:256
===========================================================


Root > 

Expected behavior

Do not crash if there is nothing to undo.

To Reproduce

Start root prompt. Press the undo shortcut. (CTRL+_).

Setup

   ------------------------------------------------------------------
  | Welcome to ROOT 6.27/01                        https://root.cern |
  | (c) 1995-2021, The ROOT Team; conception: R. Brun, F. Rademakers |
  | Built for linuxx8664gcc on Jan 12 2022, 10:17:19                 |
  | From heads/master@v6-25-01-2870-gdac9b6398d                      |
  | With c++ (Ubuntu 8.4.0-1ubuntu1~18.04) 8.4.0                     |
  | Try '.help', '.demo', '.license', '.credits', '.quit'/'.q'       |
   ------------------------------------------------------------------

Additional context

#10121