benchmark: fix timeout in write-stream-throughput

PR-URL: #17958
Fixes: #17901
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Joyee Cheung <joyeec9h3@gmail.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: Ruben Bridgewater <ruben@bridgewater.de>

benchmark/fs/write-stream-throughput.js

@@ -41,10 +41,6 @@ function main(conf) {
   var started = false;
   var ending = false;
   var ended = false;
-  setTimeout(function() {
-    ending = true;
-    f.end();
-  }, dur * 1000);
 
   var f = fs.createWriteStream(filename);
   f.on('drain', write);
@@ -66,6 +62,10 @@ function main(conf) {
 
     if (!started) {
       started = true;
+      setTimeout(function() {
+        ending = true;
+        f.end();
+      }, dur * 1000);
       bench.start();
     }