Avoid crash if user disables Camera while Gallery is open

We cache the camera availability check so in the corner case that
a user disables their camera in package manager, avoid crashing.
Not necessary to do more sophisticated handling since this is a
narrow case initiated by user.

Bug: 11435559
Change-Id: I54d5015cdd9b64aec5c9da9a393824d3b41201a1
1 file changed