QApplication::topLevelWidgets Crashes

Call QApplication::topLevelWidgets() crashes.

local stack:

the function is:

```cpp
QWidgetList QApplication::topLevelWidgets()
{
    QWidgetList list;
    QWidgetList all = allWidgets();

    for (QWidgetList::ConstIterator it = all.constBegin(), cend = all.constEnd(); it != cend; ++it) 

{         QWidget *w = *it;         if (w->isWindow() && w->windowType() != Qt::Desktop)             list.append(w);     }

    return list;
}
```