MAGETWO-56868: CLONE - Cannot save a product with images for the second time

- Fixed image merging problem.

Author: Hayder Sharhan

app/code/Magento/Catalog/Model/Product.php

@@ -1468,7 +1468,10 @@ public function getMediaGalleryImages()
         if (!$this->hasData('media_gallery_images') && is_array($this->getMediaGallery('images'))) {
             $images = $this->_collectionFactory->create();
             foreach ($this->getMediaGallery('images') as $image) {
-                if ((isset($image['disabled']) && $image['disabled']) || empty($image['value_id'])) {
+                if ((isset($image['disabled']) && $image['disabled'])
+                    || empty($image['value_id'])
+                    || $images->getItemById($image['value_id']) != null
+                ) {
                     continue;
                 }
                 $image['url'] = $this->getMediaConfig()->getMediaUrl($image['file']);