url: fix off-by-one error in loop handling dots

Fixes an error where a loop, used to traverse an array of length `n`,
ran `n + 1` times instead of `n`.

PR-URL: https://github.com/nodejs/node/pull/8420


Reviewed-By: Brian White <mscdex@mscdex.net>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Sakthipriyan Vairamani <thechargingvolcano@gmail.com>