Fix archive containing a single invalid symbol

[susematz]

If an archive contains a single symbol whose target doesn't exist
(like gcc's libgo testsuite for the tar module) then neither
ref $unpacked nor -e $unpacked is true (because unpacking causes
no error, but still the file doesn't exist in -e parlance). The
if cascade after it explicitely checks for symlink-ness of
$unpacked and does the right thing (removing it), so just don't
die prematurely if $unpacked is a symlink.

[kraih]

Nice find and explanation. 👍

[susematz]

Yeah, well, I'm very interested in gcc7 progressing in legaldb ;-)
Now if I only hadn't fat-fingered symlink for symbol in comment and commit subject :-/ No matter, not
worth it to amend and resubmit.