Don't wait for visible if there is no running activity left.

We could run into this situation on some devices (eg. clockworks),
the next activity doesn't get launched until we destroy this one.

allResumedActivitiesVisible() will return false if there is no other
activity running at all. Check top running activity and it's visibility
instead.

bug: 28400334
Change-Id: Ib8957e499580a10206fdd4e27da19fbc2bdb5843