Fixing NullPointerException in TaskbarUIController

Test: Presubmit
Bug: 322617093
Flag: NONE
Change-Id: I648ff17bbc666f30bd43fdab3320d058ac9e1f9f

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

@@ -93,6 +93,7 @@ public class TaskbarUIController {
     public void onTaskbarIconLaunched(ItemInfo item) {
         // When launching from Taskbar, e.g. from Overview, set FLAG_IN_APP immediately instead of
         // waiting for onPause, to reduce potential visual noise during the app open transition.
+        if (mControllers.taskbarStashController == null) return;
         mControllers.taskbarStashController.updateStateForFlag(FLAG_IN_APP, true);
         mControllers.taskbarStashController.applyState();
     }