QTreeViewPrivate::updateScrollBars depends on a correctly set up
viewItems vector. If a delayed layout is pending, we must call
QTreeViewPrivate::executePostedLayout before accessing any stored model
indices.
Task-number: QTBUG-45697
Change-Id: I55fcbaf81f225b26181c2cf739283740b85dd16a
Reviewed-by: Friedemann Kleint <Friedemann.Kleint@theqtcompany.com>
Reviewed-by: Olivier Goffart (Woboq GmbH) <ogoffart@woboq.com>