Symbian camera backend does not reclaim resources when returning to foreground

Using the declarative-camera example, this can be reproduced in two ways:

1. Launch declarative-camera
2. Lock the screen
3. Unlock the screen
   Sometimes, the viewfinder returns to the screen; on other occasions, it does not. When the viewfinder is not restored, the following message is printed to the log:

   Camera error: "Access to camera device was rejected."
   

The other way to reproduce the defect is:

1. Launch declarative-camera
2. Press the camera hardware key, which causes the built-in camera app to launch
3. Close the built-in camera app
   declarative-camera comes back to the foreground, but the viewfinder is not restarted.