PlayerService: runtime-assert that we get passed a service

We directly call the `getService` function after receiving the
argument, so resolving the WeakPointer should never return `null` in
our case.
Of course there could be a race condition in theory, but I feel like
if that happens we have bigger problems?

Author: Profpatsch

app/src/main/java/org/schabi/newpipe/player/PlayQueueActivity.java

@@ -220,11 +220,18 @@ public void onServiceDisconnected(final ComponentName name) {
             }
 
             @Override
-            public void onServiceConnected(final ComponentName name, final IBinder service) {
+            public void onServiceConnected(final ComponentName name, final IBinder binder) {
                 Log.d(TAG, "Player service is connected");
 
-                if (service instanceof PlayerService.LocalBinder) {
-                    player = ((PlayerService.LocalBinder) service).getService().getPlayer();
+                if (binder instanceof PlayerService.LocalBinder) {
+                    @Nullable final PlayerService s =
+                            ((PlayerService.LocalBinder) binder).getService();
+                    if (s == null) {
+                        throw new IllegalArgumentException(
+                                "PlayerService.LocalBinder.getService() must never be"
+                                        + "null after the service connects");
+                    }
+                    player = s.getPlayer();
                 }
 
                 if (player == null || player.getPlayQueue() == null || player.exoPlayerIsNull()) {

app/src/main/java/org/schabi/newpipe/player/helper/PlayerHolder.java

@@ -188,17 +188,23 @@ public void onServiceConnected(final ComponentName compName, final IBinder servi
             }
             final PlayerService.LocalBinder localBinder = (PlayerService.LocalBinder) service;
 
-            playerService = localBinder.getService();
+            @Nullable final PlayerService s = localBinder.getService();
+            if (s == null) {
+                throw new IllegalArgumentException(
+                        "PlayerService.LocalBinder.getService() must never be"
+                                + "null after the service connects");
+            }
+            playerService = s;
             if (listener != null) {
-                listener.onServiceConnected(playerService);
+                listener.onServiceConnected(s);
                 getPlayer().ifPresent(p -> listener.onPlayerConnected(p, playAfterConnect));
             }
             startPlayerListener();
             // ^ will call listener.onPlayerConnected() down the line if there is an active player
 
             // notify the main activity that binding the service has completed, so that it can
             // open the bottom mini-player
-            NavigationHelper.sendPlayerStartedEvent(localBinder.getService());
+            NavigationHelper.sendPlayerStartedEvent(s);
         }
     }