Short multiline chat messages are ignored by SD

[CoconutMacaroon]

What problem has occurred?

If you send a short multiline chat command to SD (such as !!/location with some text on a new line), it gets ignored if it would fit in a normal single line message. This came up in the context of a different issue also about multiline messages, and it would be helpful to know if this should be fixed alongside/before that or if this can be considered "won't fix"/"deferred".

I suspect enabling support itself wouldn't be hard, but I don't know is what the side effects of doing so would be.

My theory is here. Cody Gray helped figure this out. However, I haven't validated that theory with a debugger, so it may be wrong.

See also #12732

What would you like to happen/not happen?

A decision is made on whether this should be fixed and these commands are processed (knowing this may cause more bugs) or this is considered something that won't be fixed and I'll remove it as a blocker on the issue/PR with multiline messages.

I don't really have a preference.