(android) Fix NullPointerException in AudioPlayer.readyPlayer

 This closes apache#129

Author: TommiKetola

src/android/AudioPlayer.java

@@ -590,7 +590,7 @@ private boolean readyPlayer(String file) {
                     return true;
                 case MEDIA_STOPPED:
                     //if we are readying the same file
-                    if (this.audioFile.compareTo(file) == 0) {
+                    if (file!=null && this.audioFile.compareTo(file) == 0) {
                         //maybe it was recording?
                         if (player == null) {
                             this.player = new MediaPlayer();