[Perl/perl5] d9dc5f: Add boolean cast to ndbm_EXISTS

[Dagfinn Ilmari Mannsåker via perl5-changes]

  Branch: refs/heads/blead
  Home:   https://github.com/Perl/perl5
  Commit: d9dc5fe738695a076787b70f8768b8327b88c148
      
https://github.com/Perl/perl5/commit/d9dc5fe738695a076787b70f8768b8327b88c148
  Author: Dagfinn Ilmari Mannsåker <ilm...@ilmari.org>
  Date:   2023-08-09 (Wed, 09 Aug 2023)

  Changed paths:
    M ext/NDBM_File/NDBM_File.pm
    M ext/NDBM_File/NDBM_File.xs

  Log Message:
  -----------
  Add boolean cast to ndbm_EXISTS

The AIX compiler yields a warning when assigning the void* from
dbm_fetch(...).dptr to the bool RETVAL, so wrap the call in
cBOOL(...).