- Check that the chunk_size is at least 1 byte
- Split out the chunk loop from the unicode code point backtracking
    so that the bounds check is not performed on every loop.
    Also labeled the loops because it's prettier that way.
- Remove redundant vectorization of iterator
- Change error messages to be less confusing
Still looking for ways to reorganize this code to be a little easier
on the eyes.

…usize::MAX