Fixes crash from selecting uninstalled app info from recents.

- when the package is uninstalled, also remove it from the recent tasks
- move retrieveAppEntry() from onCreate() to getPreferenceControllers()
so that if the package info is invalid, do not create any controllers,
as the activity will be finished anyway.

Change-Id: Ibbfa16e3d1f941a0a200e78ec73a06ca8511f82b
Fixes: 72656345
Test: make RunSettingsRoboTests