camera: Fix camera startup racing with orientation change

 * When launching the camera via the lock screen widget on some devices,
   the orientation change shows up late, and we get an
   onConfigurationChanged in the middle of setting up the textures,
   causing an infinite wait in the UI thread.
 * Ignore these events until the preview is up and running, orientation
   will be checked later.

Change-Id: Icf5013e039324d617acd1c1108d37c655776c1c3