Function answer_of 

pub fn answer_of(
    line: &PorchLine,
    group: &[&Line],
    o: &Offer<'_>,
) -> Option<Answer>

A Porch’s line’s answer (line, of the messages group, oldest first): none for a code’s line, nor for lines from a phone that names no notification (an older Sioul’s: Text back as before).