[Perl/perl5] bb1dc6: Check for NULL locale in S_emulate_setlocale

[Hugo van der Sanden via perl5-changes]

  Branch: refs/heads/hv/safelocale
  Home:   https://github.com/Perl/perl5
  Commit: bb1dc64425cb8e81a2e70127ba3bbd2f3cd02a91
      
https://github.com/Perl/perl5/commit/bb1dc64425cb8e81a2e70127ba3bbd2f3cd02a91
  Author: Hugo van der Sanden <h...@crypt.org>
  Date:   2021-09-12 (Sun, 12 Sep 2021)

  Changed paths:
    M locale.c

  Log Message:
  -----------
  Check for NULL locale in S_emulate_setlocale

gcc-11.2.0 correctly warns that it is called with NULL from
Perl_switch_to_global_locale().