pub fn move_prev(&mut self) {
        match self.current.take() {
            // No current. We're at the start of the list. Yield None and jump to the end.
            None => {
                self.current = self.list.tail;
                self.index = self.list.len().checked_sub(1).unwrap_or(0);
            }
            // Have a prev. Yield it and go to the previous element.
            Some(current) => unsafe {
                self.current = current.as_ref().prev;
                self.index = self.index.checked_sub(1).unwrap_or_else(|| self.list.len());
            },
        }
    }
Moves the cursor to the next element of the `LinkedList`.

If the cursor is pointing to the "ghost" non-element then this will move it to
the
benchmarks/haystacks/code/rust-library.rs