Add Null check in AppWindowToken.onDisplayChanged.

Since onDisplayChanged is through DisplayManagerGlobal.sendDisplayEvent
by message, we should check all objects if is null in onDisplayChanged
to prevent message delayed case.

Bug: 119926469
Test: All existing tests passed
Change-Id: Icf5d8b19384ee0a569b6402970a8fc0bca1c882c
1 file changed