Avoid conflict surface reset on auto-enter-pip

This fix was introduced in ag/16150706 and recently got overridden with
ag/18751998, UnfoldAnimationController#resetTask happens in between
RecentsAnimationController cleanup and PipTaskOrganizer#onTaskAppeared
may cause flicker at the end of auto-enter-pip transition.

Fix it by intentionally ignore resetSurface if the task's pinned.

Bug: 235737615
Test: auto enter pip repeatedly on foldable
Test: atest WMShellUnitTests:UnfoldAnimationControllerTest
Change-Id: I5de034f5c0d3f150dd77aadb97c0d2b3f9c64c15