Don't reset cached room list values when they are falsey
`unread` and `unread-muted` store booleans in the cache, and can easily be `false`. Without this patch, both of those cached types would be cleared from the object where a later call to `getRoomState` would try and re-populate them. `getRoomState` is supposed to use the cache where possible to avoid making the more expensive calls required to calculate those booleans.
On my account in a test environment, this brings the `generateRoomLists` execution time down from ~250ms to just ~30ms.
This still does not solve the whole issue, but should solve the more common case of performance woes for people.