Ensure disp_class cannot be None in DispatchWithEvents and WithEvents

[Avasam]

If gencache.GetClassForProgID returns None, the error message is now a clearer TypeError instead of the previous generic AttributeError: 'NoneType' object has no attribute 'CLSID'

[mhammond]

thanks! This could all still stay in that inner if block

[Avasam]

Technically yes, but neither mypy nor pyright seem to see that disp_class cannot be None if I raise after the try-except in the if branch.
Some likely relevant issues:

• [possibly-undefined] False-positive with nested try block and finally python/mypy#14309
• Making a variable optional in an else block doesn't work for try/else python/mypy#12782
• Inference in the else block of a try-except-else python/mypy#14527

[Avasam]

Deduplicating code between DispatchWithEvents and WithEvents resolved this anyway

[mhammond]

damn! But fair enough I guess...

[Avasam]

I noticed the code was near-identical in another function and that this improvement could apply to it as well. So I combined the code in a different method which also resolves the type-narrowing issue. Please let me know if this change suits you.

[Avasam]

Not necessary for this change. It just helped be make sense of, and validate the type narrowing.