Re-initialize the DemoApp player on BLWE

This CL shows a de facto way to solve BLWEs until an in-player
solution is implemented.

Issue:#1782

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Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=145265895

demo/src/main/java/com/google/android/exoplayer2/demo/PlayerActivity.java

@@ -461,11 +461,12 @@ public class PlayerActivity extends Activity implements OnClickListener, ExoPlay
     playerNeedsSource = true;
     if (isBehindLiveWindow(e)) {
       clearResumePosition();
+      initializePlayer();
     } else {
       updateResumePosition();
+      updateButtonVisibilities();
+      showControls();
     }
-    updateButtonVisibilities();
-    showControls();
   }
 
   @Override