fix for #79217, scrollbar position need to be invalidated when switching folders.

r=hwaara,sspitzer sr=hyatt.  fix by Jan Varga (varga@utcru.sk)

layout/xul/base/src/outliner/src/nsOutlinerBodyFrame.cpp

@@ -497,6 +497,9 @@ NS_IMETHODIMP nsOutlinerBodyFrame::SetView(nsIOutlinerView * aView)
     // The scrollbar will need to be updated.
     InvalidateScrollbar();
 
+    // Reset scrollbar position.
+    UpdateScrollbar();
+
     PRInt32 rowCount;
     mView->GetRowCount(&rowCount);
     SetVisibleScrollbar((rowCount >= mPageCount));

layout/xul/base/src/tree/src/nsTreeBodyFrame.cpp

@@ -497,6 +497,9 @@ NS_IMETHODIMP nsOutlinerBodyFrame::SetView(nsIOutlinerView * aView)
     // The scrollbar will need to be updated.
     InvalidateScrollbar();
 
+    // Reset scrollbar position.
+    UpdateScrollbar();
+
     PRInt32 rowCount;
     mView->GetRowCount(&rowCount);
     SetVisibleScrollbar((rowCount >= mPageCount));