errors: provide defaults for unmapped uv errors

libuv does not map 100% of errors. When an unmapped error is
encountered, the Map returns undefined, which is then
unsuccessfully destructured, causing an exception. This commit
adds a default value in the event of an unmapped error.

PR-URL: https://github.com/nodejs/node/pull/29288


Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: Ben Noordhuis <info@bnoordhuis.nl>