The code has apparently been broken for quite a while, probably since
the change that made the QObject constructor invokable.
Fixes: QTBUG-91710
Pick-to: 6.0 6.1 5.15
Change-Id: I8b7e6c8a579913b3d0e2a364ffdbffe8d404c72b
Reviewed-by: Edward Welbourne <edward.welbourne@qt.io>