cc @mattiZed

Repro (note ommission of should_panic directive on the test: we want to ensure that error values and panics are surfaced, and we want to distinguish between them, since we can handle errors, but not panics). We expect this test to return an Err value, but we have a logic error in our loop beginning on line 141:

#[test]
fn invalid_string() {
    let s = "ugh_ugh";
    let expected: Result<_, _> = Err("Cannot decode character at index 12".to_string());
    assert_eq!(decode_polyline(s, 5), expected);
}

Well then, I guess it's time to fix the algorithm instead of suppressing the symptoms - I might have a bit of free time for this next week as my org also relies on this crate in some sense.