rust-clippy: factor an `if` with the same duplicated clause Unlike the next changeset, this if is not really made clearer by keeping the cases separate.

rust: fix broken debug assertions These were caught by `clippy`. It appears no one uses the debug builds, which is how this wasn't caught before.

rust-narrow: fix loop that never loops This was caught by `clippy`. I guess the narrow tests leave something to be desired, since this previously only checked the first valid pattern.