Fix reload bug

[SerraPi]

let index = match index {
    Some(index) => index - 1,
    None => {
        lock!(map).push(monitor_name.clone());
        lock!(map).len() - 1
    }
};

//This causes index to underflow
//Expected Output is something like 0, 1, etc
//But sometimes we go back around to 18446744073709551615

//Removing the index -1 here seems to work ok with multi monitor, and reload is not broken anymore

Fixes #598