[Perl/perl5] 2753cc: locale.c: Fix S get_displayable string()

[Karl Williamson via perl5-changes]

  Branch: refs/heads/blead
  Home:   https://github.com/Perl/perl5
  Commit: 2753ccd71ad42502818a8851ddc1c2f182e2879e
      
https://github.com/Perl/perl5/commit/2753ccd71ad42502818a8851ddc1c2f182e2879e
  Author: Karl Williamson <k...@cpan.org>
  Date:   2023-08-09 (Wed, 09 Aug 2023)

  Changed paths:
    M locale.c

  Log Message:
  -----------
  locale.c: Fix S get_displayable string()

This fixes the errors that Tony Cook pointed out in
https://github.com/Perl/perl5/pull/21346,
and returns "" for an empty string.