fix a lack of early error in Iterator.concat polyfill on primitive as an iterator

Author: zloirock

CHANGELOG.md

@@ -15,6 +15,7 @@
 - Fixed iterator closing in `Array.from` polyfill on failure to create array property
 - Fixed handling strings as iterables in `Iterator.{ zip, zipKeyed }` polyfills
 - Fixed some cases of iterators closing in `Iterator.{ zip, zipKeyed }` polyfills
+- Fixed a lack of early error in `Iterator.concat` polyfill on primitive as an iterator
 - Fixed iterator closing in `Set.prototype.{ isDisjointFrom, isSupersetOf }` polyfill
 - Fixed (updated following the final spec) one more case `Set.prototype.difference` polyfill with updating `this`
 - Fixed `DataView.prototype.setFloat16` polyfill in (0, 1) range

packages/core-js/modules/es.iterator.concat.js

@@ -21,7 +21,7 @@ var IteratorProxy = createIteratorProxy(function () {
       }
       var entry = iterables[iterableIndex];
       this.iterables[iterableIndex] = null;
-      iterator = this.iterator = call(entry.method, entry.iterable);
+      iterator = this.iterator = anObject(call(entry.method, entry.iterable));
       this.next = iterator.next;
     }
     var result = anObject(call(this.next, iterator));