Set display change ready only if no one sets

Otherwise it will break some cases explicitly set ready to false,
such as if there is activity switch.

Bug: 268506437
Test: atest NexusLauncherTests:TaplTestsLauncher3
Test: Simulate the sequence: setRequestedOrientation()
       -> finishActivity() -> startTransition().
      The task surface should be visible.
Change-Id: Ie76092420a9285401818fd96fe36971e2890cb3d