Fix case in which onTaskStackChanged was not called

In completeResumeLocked, visibility was changed but we didn't set the
flag so the listeners didn't get notified.

Test:
runtest -c com.android.server.am.TaskStackChangedListenerTest frameworks-services

Change-Id: I4b4076a895baafc877f312d24211a2fc69a98e3b
Fixes: 31527783