Writing for the first time in your session in a room can throw an error

[bwindels]

When none of your syncs so far contained your own member event for a room (because of lazy loading), fetching it when you open the timeline will create a RoomMember object with null for data, which throws an error when calling PendingEventEntry.sender.

We should probably fall back to your userId and once you write it will get updated.

[bwindels]

I think this was likely in part caused by the same issue that caused #271, e.g. the member not being written because it was already added to the cache by lookupMember. We should still fall back to the user id though.

[bwindels]

I made a fix at https://github.com/vector-im/hydrogen-web/commits/bwindels/fetch-member-on-first-msg before realizing #271 is likely the root cause. I think that fix adds a bit too much fluff for something that doesn't really happen in practice, so I will go with just fall back to the user id. If we then in practice see the first message being locally echod with just the user id, we know the more involved fix is needed, but I doubt it.