Fix builtin checkout crashing when given an invalid path

Signed-off-by: Alex Riesen <raa.lkml@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

builtin-checkout.c

@@ -545,6 +545,10 @@ int cmd_checkout(int argc, const char **argv, const char *prefix)
 
 	if (argc) {
 		const char **pathspec = get_pathspec(prefix, argv);
+
+		if (!pathspec)
+			die("invalid path specification");
+
 		/* Checkout paths */
 		if (opts.new_branch || opts.force || opts.merge) {
 			if (argc == 1) {