report: do not use `uv_default_loop()` as fallback

Not seeing an associated `Environment` is a rare condition anyway,
but using `uv_default_loop()` as a fallback is not thread-safe.

PR-URL: https://github.com/nodejs/node/pull/25652


Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Gireesh Punathil <gpunathi@in.ibm.com>