path_ignore_case fails with a non-ASCII first character

[5225225]

test case:

#[test]
fn test_non_ascii() {
    let mut tree = Node::new();
    tree.insert("x:x", ());
    tree.path_ignore_case("£", false);
}

[ibraheemdev]

Oddly, this passes:

#[test]
fn test_non_ascii() {
    let mut tree = Node::new();
    tree.insert("x:x", ());
    tree.path_ignore_case("/£", false);
}