Use correct 1-1 room avatar after users leave

[lukebarnard1]

The correct 1-1 avatar is used with rooms in which there are only two users with either "join" or "invite" as their membership (importantly, not "leave" or otherwise).

(This is important when a user moves accounts and re-joins previously left 1-1 chats)

[ara4n]

will this not have the side-effect that if i'm in a 1:1 with someone and they leave, the icon will change to just be me, rather than showing them? This will be quite unintuitive, given the history is with them...

[ara4n]

lgtm, assuming this matches the logic for calculating the name. (it feels wrong that these are maintained entirely separately........)

[lukebarnard1]

It would be nice to push this sort of stuff back up to the js-sdk somehow.

I'm now thinking that leftUserIds should probably only contain users that actually left... If there's one person in the room and one person got kicked, they should probably not be the room avatar?... The spec says (and this makes a lot of sense) that you should only " consider m.room.member events for users other than the logged-in user, with membership: join or membership: invite. i.e. other members should be totally ignored.

TL;DR this PR currently ignores the room name spec. If we want to consider users that have left, we need to update the spec really.

[lukebarnard1]

Closing as this is an obscure edge-case of swapping accounts

[lukebarnard1]

FTR @dbkr looked this over and gave the go-ahead.

[lukebarnard1]

I'm going to merge this, knowingly excluding it from Riot 14 so that we can necessary QA on it.