[Perl/perl5] fe048c: Revert "locale.c: Don't use SvPVX .." and replace

[Karl Williamson via perl5-changes]

  Branch: refs/heads/blead
  Home:   https://github.com/Perl/perl5
  Commit: fe048cfaa3b42320785bd0c34896ac834634db22
      
https://github.com/Perl/perl5/commit/fe048cfaa3b42320785bd0c34896ac834634db22
  Author: Karl Williamson <k...@cpan.org>
  Date:   2023-10-30 (Mon, 30 Oct 2023)

  Changed paths:
    M locale.c

  Log Message:
  -----------
  Revert "locale.c: Don't use SvPVX .." and replace

Commit 2f1617ef716ae12369475fa6c11cbefd7ba7dfca works but under
Configurations compiled with -DNO_LOCALE_NUMERIC or
-DNO_LOCALE_MONETARY, "uninitialized" errors are emitted.

Revert that commit, and instead test for SvPOK before getting to the
spot where the value would be used.