Fix crash due to use of native widgets on Windows

Qt has corner cases when all of its widgets are native widgets.
This particular crash was a loop between QWidget::create()
and QWidget::createWinId().

src/private/DragController.cpp

@@ -788,6 +788,12 @@ static QWidgetOrQuick *qtTopLevelForHWND(HWND hwnd)
             // Case not supported for QtQuick.
             const QWidgetList widgets = qApp->topLevelWidgets();
             for (QWidget *widget : widgets) {
+                if (!widget->windowHandle()) {
+                    // Don't call winId on windows that don't have it, as that will force all its childrens to have it,
+                    // and that's not very stable. a top level might not have one because it's being destroyed, or because
+                    // it's a top-level just because it has't been reparented I guess.
+                    continue;
+                }
                 if (hwnd == ( HWND )widget->winId()) {
                     return widget;
                 }