accept null longopts pointer in getopt_long

this is an undocumented feature of GNU getopt_long that the BSD
version also mimics, and is reportedly needed by some programs.

src/misc/getopt_long.c

@@ -52,7 +52,7 @@ static int __getopt_long(int argc, char *const *argv, const char *optstring, con
 static int __getopt_long_core(int argc, char *const *argv, const char *optstring, const struct option *longopts, int *idx, int longonly)
 {
 
-	if (argv[optind][0] == '-' &&
+	if (longopts && argv[optind][0] == '-' &&
 		((longonly && argv[optind][1]) ||
 		 (argv[optind][1] == '-' && argv[optind][2])))
 	{