fix nocopy of mutex

ui/browsing/trackspage.go

@@ -26,9 +26,9 @@ type TracksPage struct {
 	title           *widget.RichText
 	searcher        *widgets.SearchEntry
 	tracklist       *widgets.Tracklist
-	loader          widgets.TracklistLoader
+	loader          *widgets.TracklistLoader
 	searchTracklist *widgets.Tracklist
-	searchLoader    widgets.TracklistLoader
+	searchLoader    *widgets.TracklistLoader
 	playRandom      *widget.Button
 	container       *fyne.Container
 }

ui/widgets/tracklistloader.go

@@ -21,7 +21,7 @@ type TracklistLoader struct {
 	highestShown int
 }
 
-func NewTracklistLoader(tracklist *Tracklist, iter mediaprovider.TrackIterator) TracklistLoader {
+func NewTracklistLoader(tracklist *Tracklist, iter mediaprovider.TrackIterator) *TracklistLoader {
 	t := TracklistLoader{
 		tracklist: tracklist,
 		iter:      iter,
@@ -29,7 +29,7 @@ func NewTracklistLoader(tracklist *Tracklist, iter mediaprovider.TrackIterator)
 	t.tracklist.OnTrackShown = t.onTrackShown
 	t.fetching = true
 	go t.loadMoreTracks(25)
-	return t
+	return &t
 }
 
 // Cancels all asynchronous loads so that they will no longer modify the tracklist.