[Perl/perl5] ef4802: utf8_hop_back: Check before derefencing

[Karl Williamson via perl5-changes]

  Branch: refs/heads/blead
  Home:   https://github.com/Perl/perl5
  Commit: ef4802ef98d93b7e79e66c7b4682cbbf6a50214f
      
https://github.com/Perl/perl5/commit/ef4802ef98d93b7e79e66c7b4682cbbf6a50214f
  Author: Karl Williamson <k...@cpan.org>
  Date:   2023-07-17 (Mon, 17 Jul 2023)

  Changed paths:
    M inline.h

  Log Message:
  -----------
  utf8_hop_back: Check before derefencing

This conditional derefenced before checking if it is safe to dereference