Comment 5 for bug 1393749

We could do a search for tracks in when the coverartcache hits a track with an UNKOWN source.

I'm not sure how we should handle the writes to our database. The easiest is to make one write per track that we discover with an UNKOWN source. If someone drops a ton of tracks then we will also have a lot of writes to the database. We could also decide that we don't care about that and just do it anyway assuming nobody will drop a large amount of external tracks.