Change onTaskInfoChanged to only use display id from task info.

Fixes a potential NPE where task appears before display and does not
have a valid Display object to reference.

Bug: b/264218571
Test: atest
MultiWindowTests#testDisallowReparentOperationWhenInLockedTask

Change-Id: I9191a1ee85842873bedede9745c9f9b11ea42b99