Fix __get_disp_and_event_classes early return of a single element

[davimed]

Ensure that __get_disp_and_event_classes returns a tuple of three elements, as expected by WithEvents and DispatchWithEvents.

[mhammond]

@Avasam this is a regression from #2322?

[Avasam]

@Avasam this is a regression from #2322?

Yes.

This current PR duplicates the code of the non-if branch. Which was one of the point of splitting this off in a separate function in the first place.

See #2491 which produces the same fix without duplication.

[Avasam]

This should be fixed by #2491 😃