split at safe always splits at the same point

[aeosynth]

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Hi, split_at_safe appears to be broken, always splitting at 3 characters to eot.

use unicode_linebreak::split_at_safe;

fn main() {
    let v = vec!["testing", "4321", "a longer sentence 987654321"];

    for s in v {
        let (prev, safe) = split_at_safe(s);
        println!("{}={}", prev, safe);
    }
}

results

test=ing
4=321
a longer sentence 987654=321