fix bugs with reordering playlist tracks multiple times

ui/browsing/playlistpage.go

@@ -190,16 +190,20 @@ func (a *PlaylistPage) doSetNewTrackOrder(ids []string, newPos int) {
 		}
 	}
 	newTracks := sharedutil.ReorderItems(a.tracks, idxs, newPos)
-	ids = sharedutil.TracksToIDs(newTracks)
-	if err := a.sm.Server.ReplacePlaylistTracks(a.playlistID, ids); err != nil {
-		log.Printf("error updating playlist: %s", err.Error())
-	} else {
-		renumberTracks(newTracks)
-		// force-switch back to unsorted view to show new track order
-		a.tracklist.SetSorting(widgets.TracklistSort{})
-		a.tracklist.SetTracks(newTracks)
-		a.tracklist.UnselectAll()
-	}
+	// we can't block the UI waiting for the server so assume it will succeed
+	go func() {
+		ids = sharedutil.TracksToIDs(newTracks)
+		if err := a.sm.Server.ReplacePlaylistTracks(a.playlistID, ids); err != nil {
+			log.Printf("error updating playlist: %s", err.Error())
+		}
+	}()
+
+	renumberTracks(newTracks)
+	// force-switch back to unsorted view to show new track order
+	a.tracklist.SetSorting(widgets.TracklistSort{})
+	a.tracklist.SetTracks(newTracks)
+	a.tracklist.UnselectAll()
+	a.tracks = newTracks
 }
 
 func (a *PlaylistPage) onRemoveSelectedFromPlaylist() {