Fixes for fast-scrollbar when using work profile tabs in all apps.

- do not hide scrollbar between switching tabs
- full scrollbar height
- show predictionrow only when fully scrolled to top

Bug: 70037972
Bug: 68713881

Change-Id: Icaa434ce2726b75d22ec4ac3287ab2b0e18ce42b

src/com/android/launcher3/views/RecyclerViewFastScroller.java

@@ -141,10 +141,11 @@ public class RecyclerViewFastScroller extends View {
     }
 
     public void setRecyclerView(BaseRecyclerView rv, TextView popupView) {
-        mRv = rv;
-        if (mOnScrollListener != null) {
+        if (mRv != null && mOnScrollListener != null) {
             mRv.removeOnScrollListener(mOnScrollListener);
         }
+        mRv = rv;
+
         mRv.addOnScrollListener(mOnScrollListener = new RecyclerView.OnScrollListener() {
             @Override
             public void onScrolled(RecyclerView recyclerView, int dx, int dy) {