don't crash on All Tracks page if API call to get album tracks fails

backend/mediaprovider/subsonic/trackiterator.go

@@ -41,15 +41,19 @@ func (a *allTracksIterator) Next() *mediaprovider.Track {
 
 	// fetch next album
 	if a.curAlbum == nil || a.curTrackIdx >= len(a.curAlbum.Tracks) {
+		haveNextAlbum := false
+		for !haveNextAlbum && !a.done {
 			al := a.albumIter.Next()
 			if al == nil {
 				a.done = true
 				return nil
 			}
 			alWithTracks, err := a.s.GetAlbum(al.ID)
-		if err != nil {
+			if err != nil || alWithTracks == nil {
 				log.Printf("error fetching album: %s", err.Error())
+				continue // try next album
 			}
+			haveNextAlbum = true
 			if len(alWithTracks.Tracks) == 0 {
 				// in the unlikely case of an album with zero tracks,
 				// just call recursively to move to next album
@@ -58,6 +62,7 @@ func (a *allTracksIterator) Next() *mediaprovider.Track {
 			a.curAlbum = alWithTracks
 			a.curTrackIdx = 0
 		}
+	}
 
 	tr := a.curAlbum.Tracks[a.curTrackIdx]
 	a.curTrackIdx += 1