Fixed a bug where systemui could crash

Because the shelf could be the only visible view
and an animation happened, it could crash.

Test: Add a notification and remove it while the yTranslation changes
Change-Id: Icf47e91075437f129ad9fd7c3f206e864178a753
Fixes: 33484955

packages/SystemUI/src/com/android/systemui/statusbar/stack/StackStateAnimator.java

@@ -253,7 +253,13 @@ public class StackStateAnimator {
                     View viewAfterChangingView = noNextView
                             ? mHostLayout.getLastChildNotGone()
                             : event.viewAfterChangingView;
-
+                    if (viewAfterChangingView == null) {
+                        // This can happen when the last view in the list is removed.
+                        // Since the shelf is still around and the only view, the code still goes
+                        // in here and tries to calculate the delay for it when case its properties
+                        // have changed.
+                        continue;
+                    }
                     int nextIndex = finalState
                             .getViewStateForView(viewAfterChangingView).notGoneIndex;
                     if (ownIndex >= nextIndex) {