QFileDialog not cleaned up when parent deleted

Creating a native QFileDialog on macOS with a nested widget as parent (not the window) will crash the application if the parent widget is deleted before the dialog. 

Steps to reproduce:

• create a QFileDialog with a non-window widget as parent
• delete the parent widget

Expected behaviour:

• widget and file dialog are gone

Actual behaviour:

• widget and file dialog are cleaned up
• native file dialog is still visible
• finishing the dialog now crashes the app (use after free)

I added a simple example to showcase the issue.