Fix optional-argument handling in in-tree getopt_long().

If a long option that accepts an optional argument is given without
one, optind is advanced twice, and the following argument is
skipped.  For example, "pg_waldump --stats --limit 5" skips --limit
and interprets "5" as a non-option, so the command complains that
it cannot location WAL file "5".  The same path also returns BADARG
when optstring starts with a colon, even though nothing is missing.
To fix, handle optional arguments before the missing-argument code,
which then only needs to deal with required arguments.

This is a bug fix and could be back-patched, but since this issue
went unnoticed for 23 years, I'm not going to bother.

Author: Sehrope Sarkuni <sehrope@jackdb.com>
Reviewed-by: solai v <solai.cdac@gmail.com>
Discussion: https://postgr.es/m/CAH7T-arxDuVCSkorO%3Dk7%2BM-_JV0JFzMpN_EtKMyD2K0RDqZ2OA%40mail.gmail.com

src/bin/pg_waldump/t/001_basic.pl

@@ -340,11 +340,10 @@ sub test_pg_waldump
 	my ($stdout, $stderr);
 
 	my $result = IPC::Run::run [
-		'pg_waldump',
+		'pg_waldump', @opts,
 		'--start' => $startlsn,
 		'--end' => $endlsn,
 		'--path' => $path,
-		@opts
 	  ],
 	  '>' => \$stdout,
 	  '2>' => \$stderr;

src/port/getopt_long.c

@@ -137,8 +137,9 @@ retry:
 					{
 						if (place[namelen] == '=')
 							optarg = place + namelen + 1;
-						else if (optind < argc - 1 &&
-								 has_arg == required_argument)
+						else if (has_arg == optional_argument)
+							optarg = NULL;
+						else if (optind < argc - 1)
 						{
 							optind++;
 							optarg = argv[optind];
@@ -152,16 +153,14 @@ retry:
 								return BADARG;
 							}
 
-							if (opterr && has_arg == required_argument)
+							if (opterr)
 								fprintf(stderr,
 										"%s: option requires an argument -- %s\n",
 										argv[0], place);
 
 							place = EMSG;
 
-							if (has_arg == required_argument)
-								return BADCH;
-							optarg = NULL;
+							return BADCH;
 						}
 					}
 					else