lei note-event: ignore kw_changed exceptions

lei note-event: ignore kw_changed exceptions

The note-event worker may see changes before a Xapian shard
commit happens, meaning keyword lookups fail as a result.
Just emit the request to the lei/store worker since it's a
fairly cheap operation at this point.

We'll try harder to look for kw changes, too, since
deduplication changes may lead to multiple docids being
resolved for a single message.