Check WindowState when looking for animation.

The method setTokenVisibilityLocked returns true when animations are
delaying the exit of an app. Previously this only checked AppToken
animations but that caused exiting WindowState animations to be
ignored.

In particular if an application both hid an AppToken and then
dismissed the AppToken, the AppToken was being removed from
mClosingTokens before the animation finished. This caused
rebuildAppWindowListLocked to lose a WindowState. Furthermore
Surfaces were not being removed when a WindowState was lost and
we were leaking Surfaces.

Fixes bug 6297563.

Change-Id: Ie75c71064518199237ec4a17d3f65e2a2dd29674