Rust-Version: sorting [1,2,3] * 10 crashes

Here is the code:
```rust
let mut a = Vec::from_iter(1..=3).repeat(10);
let l = a.len();
grail_sort(&mut a, l);
```
`thread 'main' panicked at 'index out of bounds: the len is 30 but the index is 31`
