events: optimize arrayClone by copying forward

Optimize arrayClone by copying forward.

It's slightly faster (and more readable) to copy array elements
in forward direction. This way it also avoids the ToBoolean and
the postfix count operation.

PR-URL: nodejs#10571
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: Benjamin Gruenbaum <benjamingr@gmail.com>
Reviewed-By: Rich Trott <rtrott@gmail.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Franziska Hinkelmann <franziska.hinkelmann@gmail.com>

lib/events.js

@@ -477,9 +477,9 @@ function spliceOne(list, index) {
   list.pop();
 }
 
-function arrayClone(arr, i) {
-  var copy = new Array(i);
-  while (i--)
+function arrayClone(arr, n) {
+  var copy = new Array(n);
+  for (var i = 0; i < n; ++i)
     copy[i] = arr[i];
   return copy;
 }