config.c: handle lock file in error case in git_config_rename_...

We could rely on atexit() to clean up everything, but let's be
explicit when we can. And it's good anyway because the function is
called the second time in the same process, we're in trouble.

This function should not affect the successful case because after
commit_lock_file() is called, rollback_lock_file() becomes no-op,
as long as it is initialized.
Signed-off-by: NNguyễn Thái Ngọc Duy <pclouds@gmail.com>
Signed-off-by: NJunio C Hamano <gitster@pobox.com>

config.c

@@ -2314,7 +2314,7 @@ int git_config_rename_section_in_file(const char *config_filename,
 
 	if (new_name && !section_name_is_ok(new_name)) {
 		ret = error("invalid section name: %s", new_name);
-		goto out;
+		goto out_no_rollback;
 	}
 
 	if (!config_filename)
@@ -2396,6 +2396,8 @@ int git_config_rename_section_in_file(const char *config_filename,
 		ret = error_errno("could not write config file %s",
 				  config_filename);
 out:
+	rollback_lock_file(lock);
+out_no_rollback:
 	free(filename_buf);
 	return ret;
 }