Do not assign the patched speak function to None

[CyrilleB79]

Steps to reproduce the issue

• install both Baidu Translation and and Clipboard Enhancement and restart
• Press NVDA+control+f3 to reload the add-ons

Result

NVDA cannot speak anymore

Probable explanation

When multiple add-ons patch speech.speak, we cannot consider that we have a reliable order to ensure that add-on 1 patches first and unpatch last with respect to add-on 2.

Solution

Do not set the patch function variable to None. when therminating the add-on.
We probably end up with not all speak functions being unpatched, but that still much better than having an error on each speak call.

Note

With NVDA 2024.2, there will be an extension point for the speak function which will be much cleaner.

[cary-rowen]

Thanks to @CyrilleB79 for contributing to this.
I'm happy to merge it.