Stability: call stopPreview() before switching off video module.

If the preview is not stopped, the following camera operations posted
by other modules such as "apply settings" will turn camera object
in turmoil. The camera object could start throwing exception and eventually
hang.

Bug: 16300704
Bug: 17403384
Change-Id: Idd2360869d51b9dfc06309f8ac185a65add8d0c9
1 file changed