irc.isupport, announce: fix unexpected error (get) from .announce

[Exirel]

Description

Fix #2040

Checklist

• I have read CONTRIBUTING.md
• I can and do license this contribution under the EFLv2
• No issues are reported by make qa (runs make quality and make test)
• I have tested the functionality of the things this change touches

[dgw]

I have a confuse.

[Exirel]

Design consideration aside (that we should totally start to address in 8.0), I think @dgw is right that the documentation is not good enough. In an attempt to improve the situation with a small increment, I pushed a new commit with this:

It's not enough, I think a note should be added about the differences between internal representation and attributes, and we should probably give an explanation of how the isupport parser system works—even though it's all pretty internal stuff in here, and nothing will replace a good knowledge of IRC spec.

[dgw]

I've come to terms with how this interface works for 7.x, plus both of us are probably ready to move on until we start on 8.0. The documentation side might be more helpful if it placed more emphasis on interacting with bot.isupport using getattr()? But that's for a separate PR, and likely 8.0.