If you had an unsent message in a room that was in a sublist with
the 'Show rooms with unread messages first' option enabled, the
room list would show no rooms next time you restarted element and
get stuck that way.
This was because there was a different notification category for
rooms with unsent messages but the algorithm is hard-coded to add
only a fixed set of categories to its list, and it missed 'unsent',
so it NPEed when it encountered a room with an unsent message.
This just adds the category (assuming that we want to show rooms
with unsent messages first). It doesn't make it less hard-coded, or
fix the fact that an exception in the room list code causes everything
to break.
Fixes https://github.com/vector-im/element-web/issues/19373
0332bc99cb