Fix more sign conversion errors

[k3DW]

These are some more errors I'm seeing in the Unordered tests in unordered#274. This is related to #162 / #163.

I reproduced it locally with GCC 9 with the command used in the CI.

"g++-9"   -std=c++11 -fvisibility-inlines-hidden -fPIC -m64 -pthread -O3 -finline-functions -Wno-inline -Wall -Wextra -pedantic -Werror -fvisibility=hidden -Wconversion -Wfloat-equal -Wno-variadic-macros -Wshadow -Wsign-conversion -Wsign-promo -DBOOST_ALL_NO_LIB=1 -DNDEBUG   -I"."  -c -o "bin.v2/libs/unordered/test/visualization_tests.test/gcc-9/release/x86_64/cxxstd-11-iso/threading-multi/visibility-hidden/visualization_tests.o" "libs/unordered/test/debuggability/visualization_tests.cpp"

Here is a modification of the command that produces the same error on my machine, using only the Uuid library.

g++-9 -Werror -Wsign-conversion -I /mnt/d/boost libs/uuid/include/boost/uuid/uuid_io.hpp

In file included from libs/uuid/include/boost/uuid/uuid_io.hpp:9:
/mnt/d/boost/boost/uuid/uuid.hpp: In member function ‘uint8_t* boost::uuids::uuid::end()’:
/mnt/d/boost/boost/uuid/uuid.hpp:124:49: error: conversion to ‘long int’ from ‘boost::uuids::uuid::size_type’ {aka ‘long unsigned int’} may change the sign of the result [-Werror=sign-conversion]
  124 |     iterator end() noexcept { return data + size(); }
      |                                             ~~~~^~
/mnt/d/boost/boost/uuid/uuid.hpp: In member function ‘const uint8_t* boost::uuids::uuid::end() const’:
/mnt/d/boost/boost/uuid/uuid.hpp:125:61: error: conversion to ‘long int’ from ‘boost::uuids::uuid::size_type’ {aka ‘long unsigned int’} may change the sign of the result [-Werror=sign-conversion]
  125 |     const_iterator end() const noexcept { return data + size(); }
      |                                                         ~~~~^~
In file included from libs/uuid/include/boost/uuid/uuid_io.hpp:10:
/mnt/d/boost/boost/uuid/detail/to_chars.hpp: In function ‘Ch* boost::uuids::detail::to_chars(const boost::uuids::uuid&, Ch*)’:
/mnt/d/boost/boost/uuid/detail/to_chars.hpp:50:35: error: conversion to ‘long int’ from ‘std::size_t’ {aka ‘long unsigned int’} may change the sign of the result [-Werror=sign-conversion]
   50 |         std::uint8_t ch = u.data[ i ];
      |                                   ^
cc1plus: all warnings being treated as errors

[pdimov]

The operator() change is incorrect.

[k3DW]

The operator() change is incorrect.

I'll change it back.