The counter is an optimization over calling `ret.empty()`. It was
suggested that the compiler would realize `cnt` is only `0` on the first
iteration, and not actually emit the check and conditional.
This optimization was actually not triggered at all, since we
incremented `cnt` at the beginning of the first iteration. Fix it by
incrementing at the end instead.
This was reported by Github user "Janus".
00897d0677