Clear mAddingToTaskFragment when ActivityStarter is reset

Or the next launching activity could still be added to the
TaskFragment.

Bug: 244102039
Test: steps on the bug
Change-Id: I85c40a2e81ce25d305a3757c9dcc22c657765d72

services/core/java/com/android/server/wm/ActivityStarter.java

@@ -2454,6 +2454,7 @@ class ActivityStarter {
 
         mInTask = null;
         mInTaskFragment = null;
+        mAddingToTaskFragment = null;
         mAddingToTask = false;
 
         mNewTaskInfo = null;