Fix the flicker when entering PiP from Recents

Noticed onKeyguardVisibilityChanged(visible=false,
                                    occluded=false,
                                    animatingDismiss=false)
callback when entering PiP from Recents, which causes the PiP window to
be visible while it has not settled in final bounds.

Bug: 264497272
Test: repeatedly enter PiP from Recents
Test: Ensure PiP window is visible upon device unlock
Change-Id: I807a8f081001997a25aa37ab0a7d1a19ac6397ff