Assertion occurs when closing qquicknanobrowser

"Gtk: IA__gtk_widget_hide: assertion 'GTK_IS_WIDGET (widget)' failed" appears when files are selected in dialogs right after the QuickNanoBrowser is closed. I got this assertion in debug mode.

Steps to reproduce:
1, Run ./examples/webengine/quicknanobrowser/quicknanobrowser
2, Go to http://www.w3schools.com/tags/tryit.asp?filename=tryhtml_input_accept
3, Choose file or just cancel the file dialog
4, Close quicknanobrowser

Result:
[1103/032403:FATAL:browser_main_loop.cc(253)] Gtk: IA__gtk_widget_hide: assertion 'GTK_IS_WIDGET (widget)' failed [6/1912]

I attached the corresponding backtrace.

It seems the problem is that the QGtkDialogHelper::hide() function is called twice. First one is when the dialog is closed, the second one is in ~QQuickPlatformFileDialog destructor.
Maybe QGtk2Dialog::hide should not be called in ~QQuickPlatformFileDialog if It was already called it before.