navigation: don't run gesture animation if gestures are not enabled

Makes the animation when using 3 button navigation be closer to what we
have in non fallback mode, also fixing the problem when fallback recents
just started and don't have any views.

Fix 194487871
Test: manual with gestures, 2 button and 3 button nav

Change-Id: If3925d6bef1d14f51b86169d06607786972f5f1f
(cherry picked from commit 8d49c4bb29)

quickstep/src/com/android/quickstep/FallbackSwipeHandler.java

@@ -173,7 +173,9 @@ public class FallbackSwipeHandler extends
     @Override
     protected void notifyGestureAnimationStartToRecents() {
         if (mRunningOverHome) {
-            mRecentsView.onGestureAnimationStartOnHome(mGestureState.getRunningTask());
+            if (SysUINavigationMode.getMode(mContext).hasGestures) {
+                mRecentsView.onGestureAnimationStartOnHome(mGestureState.getRunningTask());
+            }
         } else {
             super.notifyGestureAnimationStartToRecents();
         }