Merge branch 'jm/branch-rename-nothing-error'

"git branch -m" without any argument noticed an error, but with an
incorrect error message.

* jm/branch-rename-nothing-error:
  branch: give better message when no names specified for rename

builtin/branch.c

@@ -904,7 +904,9 @@ int cmd_branch(int argc, const char **argv, const char *prefix)
 		if (edit_branch_description(branch_name))
 			return 1;
 	} else if (rename) {
-		if (argc == 1)
+		if (!argc)
+			die(_("branch name required"));
+		else if (argc == 1)
 			rename_branch(head, argv[0], rename > 1);
 		else if (argc == 2)
 			rename_branch(argv[0], argv[1], rename > 1);