Fix room succession not actually working

I broke this in 409b6da1 making it not possible to join a succeeding room. I decided to keep the old behavior of not prompting you to join, because:

1. You are intentionally choosing to tap the button.
2. Room successions aren't random, a privileged user in the room is creating it and there's already some implicit existing trust

(Also the current join confirmation dialog isn't useful enough yet to make an actual informed decision anyway.)