benchmark: fix async-resource benchmark

In the benchmark, because it performs asynchronous operations before
writing its HTTP replies, the underlying socket can be closed by the
peer before the response is written. Since 28e6626c, that means
that attempting to `.end()` the HTTP response results in an uncaught
exception, breaking the benchmark.

Fix that by checking whether the response object has been destroyed
or not before attempting to call `.end()`.

https://github.com/nodejs/node/issues/33591

PR-URL: https://github.com/nodejs/node/pull/33642


Reviewed-By: Benjamin Gruenbaum <benjamingr@gmail.com>
Reviewed-By: Ruben Bridgewater <ruben@bridgewater.de>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Juan José Arboleda <soyjuanarbol@gmail.com>