Ignore exit animation when view is detached from window.

After first launched activity start remove starting window, there start
a second activity with a new task, so there will trigger a open/close
task transition while playing starting window exit animation, but since
the first launched activity is going to destory, there will goes to
clear all window for that activity.
For client side we can ignore the animation after it was detached from
window.

Bug: 190040281
Test: manual
Change-Id: Idd939feb72163d585e14db480b1e374e41597928