Fix videoPreference doesn't play after swipe out of screen

- SurfaceView is destoryed but not mMediaPlayer.setSurface() again

Fixes: 145601503
Test: manual test
Change-Id: I23a0f3762a391174c6ddc98bdd220d6fa4047941

src/com/android/settings/widget/MediaAnimationController.java

@@ -98,6 +98,7 @@ class MediaAnimationController implements VideoPreference.AnimationController {
             @Override
             public boolean onSurfaceTextureDestroyed(SurfaceTexture surfaceTexture) {
                 preview.setVisibility(View.VISIBLE);
+                mSurface = null;
                 return false;
             }