fix: an album with missing tracks is wanted back by its release group, not only when it carries a release MBID (#6167)

The release id was only ever used to find the group. 238 albums matched to a
group carried none, so their losses, five of the resolver's wrong-slot
removals among them, were never fetched again.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

internal/reacquisition/sweeper.go

@@ -103,7 +103,8 @@ func (s *Sweeper) SweepOnce(ctx context.Context) error {
 // want records one album as wanted under its release group.
 func (s *Sweeper) want(ctx context.Context, q *dbq.Queries, album dbq.ListAlbumsDueReacquisitionRow, res *PassResult) error {
 	// The query already filters these out; belt and braces.
-	if album.AlbumMbid == nil || album.ArtistMbid == nil {
+	hasGroup := album.AlbumReleaseGroupMbid != nil && *album.AlbumReleaseGroupMbid != ""
+	if (album.AlbumMbid == nil && !hasGroup) || album.ArtistMbid == nil {
 		return nil
 	}
 	group, err := s.albumReleaseGroup(ctx, q, album)