Refresh virtual wxListCtrl in wxMSW after deleting all its items

In principle, calling DeleteAllItems() on a virtual list control doesn't make
sense at all, but apparently people actually do it and it mostly works except
that the controls scrollbars are not updated, so add a call to Refresh() to
update them too, for consistency with DeleteItem() which similarly doesn't
make sense for virtual controls but where we also explicitly support them for
some reason.

src/msw/listctrl.cpp

@@ -1415,7 +1415,18 @@ bool wxListCtrl::DeleteAllItems()
 {
     // Calling ListView_DeleteAllItems() will always generate an event but we
     // shouldn't do it if the control is empty
-    return !GetItemCount() || ListView_DeleteAllItems(GetHwnd()) != 0;
+    if ( !GetItemCount() )
+        return true;
+
+    if ( !ListView_DeleteAllItems(GetHwnd()) )
+        return false;
+
+    // Virtual controls don't refresh their scrollbar position automatically,
+    // do it for them when clearing them.
+    if ( IsVirtual() )
+        Refresh();
+
+    return true;
 }
 
 // Deletes all items