/unclearallbricks. And if you actually meant to clear it but thought you didn't but uncleared anyways, /clearallunclearedbricks. If all else fails use /clearnobricks in the future to ensure that no bricks are cleared.
There's also a hidden command not many people know about called /clearsomebricks which is a pretty safe command to use because it only clears some of the bricks so if you ever regret it later you'll still have some bricks remaining. Really saved my life too many times, that command