QWidget still receives signals from children in its QObject dtor

In short:

1. Widget creates a child QStackedWidget
2. Other widgets, grandchildren of the first one, are added to the QStackedWidget
3. The `destroyed` signal of the grandchildren is connected to the grandparent
4. Grandparent is destroyed, and thus its lineage
5. Grandparent receives the `destroyed` signal of each grandchild while within its QObject dtor.

I'll attach an example once I get a bug number.

(For the record, this goes back to at least 5.11.2, according to Choqok Bug #400117.)