Array.prototype.{reduce, reduceRight}: Wrong order of operations when determining initial value.

src/array.js

Index: src/array.js
diff --git a/src/array.js b/src/array.js
index 44deff7de42c60986741615b1be389f9668dbf85..c50a2926395dd8dcf9009c3e136f89871e363895 100644
--- a/src/array.js
+++ b/src/array.js
@@ -1398,9 +1398,8 @@ function ArrayReduce(callback, current) {
   var i = 0;
   find_initial: if (%_ArgumentsLength() < 2) {
     for (; i < length; i++) {
-      current = array[i];
-      if (!IS_UNDEFINED(current) || i in array) {
-        i++;
+      if (i in array) {
+        current = array[i++];
         break find_initial;
       }
     }
@@ -1435,9 +1434,8 @@ function ArrayReduceRight(callback, current) {
   var i = length - 1;
   find_initial: if (%_ArgumentsLength() < 2) {
     for (; i >= 0; i--) {
-      current = array[i];
-      if (!IS_UNDEFINED(current) || i in array) {
-        i--;
+      if (i in array) {
+        current = array[i--];
         break find_initial;
       }
     }