MAGETWO-95773: Credit memo is created instead of returning error via invoice refund API for Bundle product

- add error message for incorrect product items

Author: krissyhiserote

app/code/Magento/Sales/Model/Order/Creditmemo/Item/Validation/CreationQuantityValidator.php

@@ -53,6 +53,10 @@ public function validate($entity)
             return [__('The creditmemo contains product item that is not part of the original order.')];
         }
 
+        if ($orderItem->isDummy()) {
+            return [__('The creditmemo contains incorrect product items.')];
+        }
+
         if (!$this->isQtyAvailable($orderItem, $entity->getQty())) {
             return [__('The quantity to refund must not be greater than the unrefunded quantity.')];
         }

app/code/Magento/Sales/Model/Order/ItemRepository.php

@@ -228,6 +228,12 @@ private function addParentItem(OrderItemInterface $orderItem)
     {
         if ($parentId = $orderItem->getParentItemId()) {
             $orderItem->setParentItem($this->get($parentId));
+        } else {
+            foreach ($orderItem->getOrder()->getAllItems() as $item) {
+                if($item->getParentItemId() === $orderItem->getItemId()) {
+                    $item->setParentItem($orderItem);
+                }
+            }
         }
     }