test: fix flaky test-perf-hooks-histogram

Make sure the histogram containing event loop delay info is posted only
when at least one datapoint is collected.

Fixes: nodejs/node#43503

PR-URL: nodejs/node#43567
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>

test/parallel/test-perf-hooks-histogram.js

@@ -89,7 +89,12 @@ const { inspect } = require('util');
     strictEqual(data.enable, undefined);
     mc.port1.close();
   });
-  setTimeout(() => mc.port2.postMessage(e), 100);
+  const interval = setInterval(() => {
+    if (e.count > 0) {
+      clearInterval(interval);
+      mc.port2.postMessage(e);
+    }
+  }, 50);
 }
 
 {