Fixed NPE when skipping before song loaded

Author: devgianlu

player/src/main/java/xyz/gianlu/librespot/player/playback/PlayerQueueEntry.java

@@ -354,7 +354,7 @@ public void close() {
         clearOutput();
 
         try {
-            codec.close();
+          if (codec != null) codec.close();
         } catch (IOException ignored) {
         }
     }