Camera2: disable the shutter button when not previewing

Camera app will crash if the shutter button is clicked while not
previewing. Disable the shutter button in onStopPreview() as it's
called by onSurfaceTextureDestroyed().

Change-Id: Ied369610c590323b977b4ac1c3150c6c905e9466
CRs-Fixed: 669190
1 file changed