test: fix flaky test-benchmark-util

Allow for zero iterations on benchmarks with a short duration.

PR-URL: https://github.com/nodejs/node/pull/17473


Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Evan Lucas <evanlucas@me.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Michael Dawson <michael_dawson@ca.ibm.com>
Reviewed-By: Khaidi Chu <i@2333.moe>