Ensure to resume home if there is no other activity

On default display, there will always have home stack,
but home activity may not have been started yet. In that
case if we want to resume home, the home stack should
still move to front.

Fix: 118862669
Test: atest ActivityStackTests#testAdjustFocusedStackToHomeWhenNoActivity
Change-Id: I3c744f6d3adeb151eac864d88d2b195e05d2332f