dumpcpp-generated code does not compile if the typelib declares non-dispatchable interfaces

dumpcpp generates only simple QAxObject subclass for vtable-only interfaces, i.e.

// stub for vtable-only interface
class IPropertyPage : public QAxObject {};

Pointers to these classes might still be returned by other functions, so a template specialization for qMetaTypeConstructHelper needs to be present; however, dumpcpp does not generate that for vtable-only classes.