Skip updateIconAlphaForHome if Taskbar is already destroyed

Bug: 269409332
Test: Switch display with and without Tasxkbar at home and in-app, Taskbar and Hotseat visibility are correct
Change-Id: I598f618c336067bf795b77ccdf3b03f420634047

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

@@ -471,6 +471,7 @@ import java.util.StringJoiner;
         if (mControllers.taskbarActivityContext.isDestroyed()) {
             Log.e("b/260135164", "updateIconAlphaForHome is called after Taskbar is destroyed",
                     new Exception());
+            return;
         }
         mIconAlphaForHome.setValue(alpha);
         boolean hotseatVisible = alpha == 0