branch -m: handle no arg properly

Modify the option parsing heuristic to handle all -m (rename) cases,
including the no-arg case.

Previously, this "fell through" to the (argc <= 2) case and caused
segfault.

Reported-by: Stefan Näwe <stefan.naewe@atlas-elektronik.com>
Signed-off-by: Tay Ray Chuan <rctay89@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

builtin/branch.c

@@ -719,11 +719,14 @@ int cmd_branch(int argc, const char **argv, const char *prefix)
 	else if (list)
 		return print_ref_list(kinds, detached, verbose, abbrev,
 				      with_commit, argv);
-	else if (rename && (argc == 1))
-		rename_branch(head, argv[0], rename > 1);
-	else if (rename && (argc == 2))
-		rename_branch(argv[0], argv[1], rename > 1);
-	else if (argc <= 2) {
+	else if (rename) {
+		if (argc == 1)
+			rename_branch(head, argv[0], rename > 1);
+		else if (argc == 2)
+			rename_branch(argv[0], argv[1], rename > 1);
+		else
+			usage_with_options(builtin_branch_usage, options);
+	} else if (argc <= 2) {
 		if (kinds != REF_LOCAL_BRANCH)
 			die(_("-a and -r options to 'git branch' do not make sense with a branch name"));
 		create_branch(head, argv[0], (argc == 2) ? argv[1] : head,