Compare containers in mChangingContainers with Task for change transitions

Currently, it's trying to find an activity in mChangingContainers,
but as Task is added for change transitions, so it ends up getting
into the else statement and incorrectly set the animation CLOSING.

Bug: 157015435
Test: go/wm-smoke
Change-Id: I5be317f2e4adeceeeb06d4a1ec432d014685cf35