Treat setup wizard default home as null.

During setup, default home progresses setup -> null -> launcher, which
can lead us to unintentionally preload the fallback overview.

Fix: 258022658
Test: Manual
Change-Id: I952b7923b06f2d4b058f42834d1f840719c73fd0

quickstep/src/com/android/quickstep/TouchInteractionService.java

@@ -1130,6 +1130,10 @@ public class TouchInteractionService extends Service
             return;
         }
 
+        // TODO(b/258022658): Remove temporary logging.
+        Log.i(TAG, "preloadOverview: forSUWAllSet=" + forSUWAllSet
+                + ", isHomeAndOverviewSame=" + mOverviewComponentObserver.isHomeAndOverviewSame());
+
         mTaskAnimationManager.preloadRecentsAnimation(overviewIntent);
     }