docs: add throws notice for isPlaying

per external issue 33610

Change-Id: Ibd778cb4ecc5f1717fa007ac069a7b3660ec4794

media/java/android/media/MediaPlayer.java

@@ -1152,6 +1152,8 @@ public class MediaPlayer
      * Checks whether the MediaPlayer is playing.
      *
      * @return true if currently playing, false otherwise
+     * @throws IllegalStateException if the internal player engine has not been
+     * initialized or has been released.
      */
     public native boolean isPlaying();