Minor NPE

Author: devgianlu

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

@@ -485,6 +485,8 @@ private void handlePause() {
     }
 
     private void handleNext() {
+        if (tracksProvider == null) return;
+
         int newTrack = tracksProvider.getNextTrackIndex(true);
         boolean play = true;
         if (newTrack >= state.getTrackCount()) {
@@ -537,6 +539,8 @@ private void loadAutoplay() {
     }
 
     private void handlePrev() {
+        if (tracksProvider == null) return;
+
         if (getPosition() < 3000) {
             state.setPlayingTrackIndex(tracksProvider.getPrevTrackIndex());
             state.setPositionMs(0);