make hasImage always return true for ServiceAlbumWithCover (and subclasses) as they have their own way of getting covers and really want to avoid having the CoverFetcher trying to find one for them.

Avoids a really nasty infinite cover fetching loop when having a service album in the playlist. In general I really dont like this idea of autofetching covers if we dont know exactly where to get it (like some services do)