src: fix v8 local handling in node_url.cc

Calling `.As<Object>()` on a non-object aborts in debug mode,
but `node_url.cc` relied on it. Address that by using `Local<Value>`
until it has been confirmed that the handle actually is an object.

PR-URL: https://github.com/nodejs/node/pull/11064


Reviewed-By: Michal Zasso <targos@protonmail.com>
Reviewed-By: Timothy Gu <timothygu99@gmail.com>
Reviewed-By: Joyee Cheung <joyeec9h3@gmail.com>
Reviewed-By: Ben Noordhuis <info@bnoordhuis.nl>
Reviewed-By: James M Snell <jasnell@gmail.com>