Function change_line 

pub(crate) fn change_line(
    qt: &CxxQtThread<Sioul>,
    shared: &Arc<Shared>,
    uri: &str,
    shown: &str,
    label: &str,
    amount: f64,
    date: &str,
) -> String

A line of the budgets’ file changed: label, amount, date; only when it is still the line the page showed (shown: its row, JSON). Returns what went wrong, else “”.