Add NPE check in CameraTransitionCallback

CameraManager.AvailabilityCallback will notifyCameraInactive()
at initial stage, and cause NPE when mCutoutViews is NULL

Initialize mCutoutView at early stage

Bug: 151706640
Test: manual boot device
Test atest SystemUITests

Change-Id: I2008342d15bb589f85bb99fcc35ede96ef9678bd