Support a backup room ID in PermalinkCreator
In the case of room upgrades, it is possible the client is trying to render the room create event, but the user has never been in the old room. This results in an error because the PermalinkCreator cannot possibly figure out a room ID.
Instead, we'll feed the creator an alternate room ID to try if the room object can't be provided.
Fixes https://github.com/vector-im/riot-web/issues/9636
