Don't prematurely set-ready for activities not actually on top

This logic is for "continuing" a transition for an activity that
was moved-to-front of its display; however, it was checking
only for front-of-displayArea. This caused it to prematurely
set readiness

Bug: 335298137
Test: Open activity on top while another is topResumed in another DA
Change-Id: I18195d411190a206238bb67873fb63e8a5410330