Fix TaskFragment pending event not dispatch

Since ag/16226483, we defer sending TaskFragment event when the
TaskFragment is not visible, and set a defer time to task#lastActiveTime
(see #dispatchPendingEvents). However, task#lastActiveTime is only
called when TaskFragment#startPausing, so it can issue when the Task is
resumed again.

Fix: 223705682
Test: verify with Settings
Test: atest WmTests:TaskFragmentOrganizerControllerTest
Change-Id: I40798c893298b67e2cbb785f33b15f7ab8d6fc86