url: fix setting `url.search` to the empty string

PR-URL: https://github.com/nodejs/node/pull/11105
Fixes: https://github.com/nodejs/node/issues/11101
Fixes: 98bb65f6

 "url: improving URLSearchParams"
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Michaël Zasso <targos@protonmail.com>
Reviewed-By: Joyee Cheung <joyeec9h3@gmail.com>