Don't applyState if taskbar is already destroyed

Test: Open overview while unfolded, then fold; ensure hotseat remains
visible
Fixes: 260135164

Change-Id: I788a9a682a7d5fabbea7c478231fc7abe92e95b9

quickstep/src/com/android/launcher3/taskbar/TaskbarLauncherStateController.java

@@ -247,6 +247,9 @@ import java.util.StringJoiner;
     }
 
     public Animator applyState(long duration, boolean start) {
+        if (mControllers.taskbarActivityContext.isDestroyed()) {
+            return null;
+        }
         Animator animator = null;
         if (mPrevState == null || mPrevState != mState) {
             // If this is our initial state, treat all flags as changed.