Trebuchet : Wallpaper picker check if cursor null

Check if media store has any images (cursor != null).

Change-Id: Ib303b0ace9c4b834be0b61727b8512b5e326a949
Merge "Trebuchet : Wallpaper picker check if cursor null" into cm-11.0
Merge remote-tracking branch 'cm/cm-11.0' into cm-11.0