Fix issue #6373340: Cannot unlock to app if app was the...

...foreground app when the device was put to sleep

This is because of activities being kept in the stopped state
while the lock screen is shown, so we never get to the point of
it becoming visible again to know to proceed.

Just at this point consider the lock screen hidden so the
activity can be resumed and run as normal; the whole point of
this is to soon hide the lock screen, anyway.

Change-Id: I3a713a2f87b8e4412ff66724c051f09a2675be00