Fixed minor NPE

Author: devgianlu

core/src/main/java/xyz/gianlu/librespot/player/Player.java

@@ -252,13 +252,17 @@ private void handleShuffle() {
     }
 
     private void shuffleTracks(boolean fully) {
+        if (tracksProvider == null) return;
+
         if (tracksProvider.canShuffle() && tracksProvider instanceof PlaylistProvider)
             ((PlaylistProvider) tracksProvider).shuffleTracks(session.random(), fully);
         else
             LOGGER.warn("Cannot shuffle TracksProvider: " + tracksProvider);
     }
 
     private void unshuffleTracks() {
+        if (tracksProvider == null) return;
+
         if (tracksProvider.canShuffle() && tracksProvider instanceof PlaylistProvider)
             ((PlaylistProvider) tracksProvider).unshuffleTracks();
         else