This used to be a feature but kinda broke/changed when we switched to
focusing on context-aware or notable events. Basically instead of only
notable events making a room bold in the room list, it's any unread
messages now.
This is only called after we already get an event with lastEvent() so
doing it again is useless. Instead, we should refactor it to behave like
similar functions (e.g. isEventHighlighted.)
I'm 99% sure of the recent crashes we've been seeing are double-frees,
the QCache one me and Duha encountered must be one. The QCache is in
charge of the one in ContentProvider, so it will sometimes try to delete
or access something already destroyed by the QML engine.
While I'm at it, I also made sure to check every other Q_INVOKABLE to
ensure we don't hit this elsewhere.
CCBUG: 502747
