[Perl/perl5] 449cda: regcomp.c: incr ref cnt of re_intuit_string() return

[Karl Williamson]

  Branch: refs/heads/smoke-me/khw-17734
  Home:   https://github.com/Perl/perl5
  Commit: 449cda1d3dd94ec86952e99cd1bd5f04352aaaa2
      
https://github.com/Perl/perl5/commit/449cda1d3dd94ec86952e99cd1bd5f04352aaaa2
  Author: Karl Williamson <k...@cpan.org>
  Date:   2020-04-28 (Tue, 28 Apr 2020)

  Changed paths:
    M regcomp.c
    M t/re/pat_advanced.t

  Log Message:
  -----------
  regcomp.c: incr ref cnt of re_intuit_string() return

This function returns an SV that it turns out may have its reference
count decremented by a future call to re_intuit_start().  Thus, the
caller doesn't get clear title to the returned SV.  This is not
documented.

It is too late in the development cycle to properly fix this, but in
this instance, it is a simple matter to increment the ref count of the
returned scalar

This fixes #17734.