Allow fallthrough taps on Recents background to go Home

In some cases the recents view isn't entirely occupied by task views.
Taps on the empty space should take the user home, which was mostly
supported except for this small missing part.

Bug: 32101881
Test: Locally on Ryu device.
Change-Id: I264202397f7408608aa444a421765715fb1e74ba

packages/SystemUI/src/com/android/systemui/recents/grid/RecentsGridActivity.java

@@ -302,6 +302,9 @@ public class RecentsGridActivity extends Activity implements ViewTreeObserver.On
             dismissRecentsToLaunchTargetTaskOrHome();
         } else if (event.triggeredFromHomeKey) {
             dismissRecentsToHome();
+        } else {
+            // Fall through tap on the background view but not on any of the tasks.
+            dismissRecentsToHome();
         }
     }