The topic of a room should be displayed when users peek a non-peekable room

Created by @ Amandine:matrix.org.

Especially for public rooms: the topic is displayed in the directory so it definitely shouldn't be hidden if the room is not peekable for consistency. I agree it's more debatable for private rooms, but then we need consistency across private and public, and if people invite someone to join, it's hard to decide based on a room name only...