fix(cli): clear optional getopt arg

Author: onthebed

main/getopt.c

@@ -57,6 +57,7 @@ PHPAPI int php_getopt(int argc, char* const *argv, const opt_struct opts[], char
 	static char **prev_optarg = NULL;
 
 	php_optidx = -1;
+	*optarg = NULL;
 
 	if(prev_optarg && prev_optarg != optarg) {
 		/* reset the state */

sapi/cli/tests/bug21901.phpt

@@ -0,0 +1,12 @@
+--TEST--
+CLI getopt preserves empty optional long option arguments
+--ARGS--
+-d foo=bar --ini
+--FILE--
+<?php
+?>
+--EXPECTF--
+Configuration File (php.ini) Path: "%s"
+Loaded Configuration File:         %s
+Scan for additional .ini files in: %s
+Additional .ini files parsed:      %s