Fixes https://github.com/certusone/wormhole/issues/685.
Example occurrence this fixes: https://i.imgur.com/gZWKf1n.png
Possible future optimizations include:
- Ignore late messages in the processor (but we can only ignore
them post settlement time, so we need the cleanup logic regardless).
- Ignoring late observations from other nodes.
- Using the stored VAA to calculate misses.
- Drop incomplete local observations. However, this is not trivial
since we do not know the message ID for those.
commit-id:47e1e59f