Fixing issue with missing scroll bar after fast-scrolling and searching.

- This was due to us not re-attaching the thumb to the scrollbar after
  we scroll the view to the top explicitly without the user scrolling.

Bug: 23562489
Change-Id: I5932b9b3b9358e23c0ec23aa235644b4f27c43ea
diff --git a/src/com/android/launcher3/allapps/AllAppsRecyclerView.java b/src/com/android/launcher3/allapps/AllAppsRecyclerView.java
index 1cde7bf..e5f2c3c 100644
--- a/src/com/android/launcher3/allapps/AllAppsRecyclerView.java
+++ b/src/com/android/launcher3/allapps/AllAppsRecyclerView.java
@@ -102,6 +102,10 @@
      * Scrolls this recycler view to the top.
      */
     public void scrollToTop() {
+        // Ensure we reattach the scrollbar if it was previously detached while fast-scrolling
+        if (mScrollbar.isThumbDetached()) {
+            mScrollbar.reattachThumbToScroll();
+        }
         scrollToPosition(0);
     }