Fix continous playing of gesture animation video.

In the gesture settings, we listen to surface texture updates to
determine when both the view and video is ready, and we auto play the
animation video. However, sometimes, the video listener will receive
the surface texture updates after the settings activity is being paused,
in which case, the video will continue to play until the user navigate
back to that gesture settings page.

In onSurfaceTextureUpdated(), check for view visibility before we try to
update anything to avoid unnecessary operation.

Change-Id: I46474c9f461d5705f599deb8b2535d8505f2fe75
Bug: 110923173
Test: make RunSettingsRoboTests