Add null-check to "Entity Tracking Improvement"

Spigot-Server-Patches/Entity-Tracking-Improvements.patch

@@ -77,7 +77,11 @@ index 0000000000000000000000000000000000000000..00000000000000000000000000000000
 +    }
 +    private void updatePassengers(EntityPlayer player) {
 +        if (tracker.isVehicle()) {
-+            tracker.passengers.forEach((e) -> e.tracker.updatePlayer(player));
++            tracker.passengers.forEach((e) -> {
++                if (e.tracker != null) {
++                    e.tracker.updatePlayer(player);
++                }
++            });
 +            player.playerConnection.sendPacket(new PacketPlayOutMount(this.tracker));
 +        }
 +    }