Fix segfault when giving invalid long option to pkg_info.

PR:		bin/133473
Submitted by:	Rafal Grodzinski
Approved by:	ed (mentor)
MFC after:	1 week

usr.sbin/pkg_install/info/main.c

@@ -58,6 +58,7 @@ static struct option longopts[] = {
 	{ "verbose",	no_argument,		NULL,		'v' },
 	{ "version",	no_argument,		NULL,		'P' },
 	{ "which",	required_argument,	NULL,		'W' },
+	{ NULL,		0,			NULL,		0 }
 };
 
 int