chrono panics on a valid input string

[omayerg]

 use chrono::format;

fn main() {
    let p = &mut format::Parsed::new();
    format::parse(p, "MONYAŽA Šander`",
    format::StrftimeItems::new("%A, %e-%h-%y %H:%M:%S"));
    
    println!("No panic");
}

(Playground)

Expected null result, but actually it panics.
It seems chrono parser misses the case where a string starts with a valid datetime part, e.g. SUN, MON, TUE... but then have non-ascii characters. For example, running the above string without letting it start with any three letters that represents a day of week doesn't panic.

[pitdicker]

This is fixed by #1024.