Sync doesn't work very well

[fd1f]

It appears that:

• only some things make sync requests return early -- a message send will, but a room create won't
• Element (and probably other clients) don't trigger sync timeouts with the original logic (when the server is new and has no events happening at least. Is this the case in other conditions?). This causes sync to return immediately forever, and the next_batch to never bump, like you're initial syncing constantly.

I fixed the latter by forcing timeouts to be respected, but this just makes the first issue more apparent. Nobody likes waiting 30 seconds to make a room when it's actually been created already and should have come down sync.