Refactor some if-else chains to match or functions on matched item

[hashedone]

I am not a fan of this if-else chain. I am pretty sure it should be a match or even a function like MsgType::generate_message_variant(...) (not sure about this one, as maybe it is not the best place to put this).

Here you did only minimal changes on this, but let's fix it up in some later refactor (I'll create a task).

Especially since those things look identical. Really. I see the difference, but I think we could simplify it. Not mentioning last else is bullcrap here, I don't see which patterns are not covered; it frustrates me.

Originally posted by @hashedone in #156 (comment)

Also, we should take a look through the codebase to find other instances of similar chains.