Fix abusable loophole in redir
Redir used user.can as a way to stop lower auth from rediricting to
higher auth to other rooms.
However, if a user had auth over another user in a private room, this
user could redir the other user even if the latter had higher global auth
and/or was not in the room.
This commit fixes that, checking if a user is inside a room before being
able to use redir on they.