src: free memory before re-setting URLHost value

Fixes: https://github.com/nodejs/node/issues/18302

PR-URL: https://github.com/nodejs/node/pull/18357


Reviewed-By: Tiancheng "Timothy" Gu <timothygu99@gmail.com>
Reviewed-By: Anatoli Papirovski <apapirovski@mac.com>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: Tobias Nießen <tniessen@tnie.de>