Fix bug RT#114999

* fixes [RT#114999](https://rt.cpan.org/Ticket/Display.html?id=114999)
* 'gnu_compat' mode single character options with optional arguments and default values
  now return correct values when used with no argument from the CLI

lib/Getopt/Long.pm

@@ -1112,7 +1112,7 @@ sub FindOption ($$$$$) {
     if ( $gnu_compat ) {
 	my $optargtype = 0; # 0 = none, 1 = empty, 2 = nonempty
 	$optargtype = ( !defined($optarg) ? 0 : ( (length($optarg) == 0) ? 1 : 2 ) );
-	return (1, $opt, $ctl, undef)
+    return (1, $opt, $ctl, defined($ctl->[CTL_DEFAULT]) ? $ctl->[CTL_DEFAULT] : undef)
 	  if (($optargtype == 0) && !$mand);
 	return (1, $opt, $ctl, $type eq 's' ? '' : 0)
 	  if $optargtype == 1;  # --foo=  -> return nothing