Reset fast scroller when All Apps resets.

This ensures the scrollbar is not left in a bad state, in
particular if you close All Apps while still scrolling (e.g.
pressing the Home button while holding the scroll bar).

Fix: 267583704
Test: Manual
Change-Id: I0e159f8e5ed289bf1628f77eab1879743b5aea00

src/com/android/launcher3/allapps/ActivityAllAppsContainerView.java

@@ -360,6 +360,9 @@ public class ActivityAllAppsContainerView<T extends Context & ActivityContext>
                 mAH.get(i).mRecyclerView.scrollToTop();
             }
         }
+        if (mTouchHandler != null) {
+            mTouchHandler.endFastScrolling();
+        }
         if (mHeader != null && mHeader.getVisibility() == VISIBLE) {
             mHeader.reset(animate);
         }