SearchIndexAddWorker logs warnings when failing to index records

Currently on preview newly created StatisticsAnnouncements aren't finding their way into rummager, but editing that announcement then causes it to index correctly. This is part of an attempt to debug why.

Preiously, SearchIndexAddWorker would fail silently if it either couldn't find the record it was supposed to index or the record was unindexable. This PR makes it log warnings in those cases.