Camera2: fix face still display after unmark the face detect option

After unmark the face detect option, the value mFace in FaceView maybe
reset value and draw all the time.

The faces should not be draw after stopFaceDetection, so block draw the
faces after stopFaceDetection and unblock after startFaceDetection.

Change-Id: I2f8316e12ad8c7b157bc732800d9247c66a17572
CRs-Fixed: 692057
2 files changed