Allow onTaskInfoChanged dispatch immediately

When TaskOrganizerController#onTaskInfoChanged receives the request to
change aspect ratio of an existing PiP window, such request would be
queued in mPendingTaskEvents and get dispatched on the next
- RootWindowContainer#performSurfacePlacementNotrace OR
- WindowAnimator#animate

In case there is no event queued in PendingTaskEvent, we change to
dispatch the event immediately. Otherwise, the next drawn should
dispatch all pending events.

Bug: 218456378
Test: atest PinnedStackTests#testChangeAspectRationWhenInPipMode \
            WmTests:WindowOrganizerTests
Change-Id: I09b43c362013b694d13566ece42a6f5be2225108