Clear activity result when launching from lock screen.

 Bug 6710029
 When the screen is locked during video play, the activity result
 from that play will be triggered immediately when unlocking to
 camera. The result must be destroyed on unlock so that the resume
 goes to the camera rather than to the video display.

Change-Id: Ifa6f00fa1cba119d5fc6e762d1757bd6aac576f4