Work around the flicker on enter PiP for foldables

This is work around for b/311084698

We use to rely on the mIsInStateChange flag to avoid resetting the
surface of PiP task, it's broken recently. The windowing mode check here
is not ideal but it should be safe to ignore any resetting from
UnfoldAnimationController for a Task that's already pinned.

Before: http://recall/-/aaaaaabFQoRHlzixHdtY/ahJ6dpKl1ajsaReCX70Wb
After: http://recall/-/aaaaaabFQoRHlzixHdtY/cc0H4jAt0KxqzFxzkfVjk7
Flag: NONE
Bug: 311084698
Test: Manually following the reproduce steps in bug
Change-Id: I5f60b2da8eaf948145ca61fb21433f5640f1feeb