Sync with magento#9600 code

Author: kassner

app/code/Magento/Catalog/Controller/Adminhtml/Product/Initialization/Helper.php

@@ -256,13 +256,22 @@ protected function setProductLinks(\Magento\Catalog\Model\Product $product)
 
         $product = $this->productLinks->initializeLinks($product, $links);
         $productLinks = $product->getProductLinks();
+        $linkTypes = [];
+        
+        /** @var \Magento\Catalog\Api\Data\ProductLinkTypeInterface $linkTypeObject */
+        foreach ($this->linkTypeProvider->getItems() as $linkTypeObject) {
+            $linkTypes[$linkTypeObject->getName()] = $product->getData($linkTypeObject->getName() . '_readonly');
+        }
+        
+        // skip linkTypes that were already processed on initializeLinks plugins
+        foreach ($productLinks as $productLink) {
+            unset($linkTypes[$productLink->getLinkType()]);
+        }
 
         /** @var \Magento\Catalog\Api\Data\ProductLinkTypeInterface $linkType */
-        foreach ($this->linkTypeProvider->getItems() as $linkType) {
-            $readonly = $product->getData($linkType->getName() . '_readonly');
-
-            if (isset($links[$linkType->getName()]) && !$readonly) {
-                foreach ((array) $links[$linkType->getName()] as $linkData) {
+        foreach ($linkTypes as $linkType => $readonly) {
+            if (isset($links[$linkType]) && !$readonly) {
+                foreach ((array) $links[$linkType] as $linkData) {
                     if (empty($linkData['id'])) {
                         continue;
                     }
@@ -271,7 +280,7 @@ protected function setProductLinks(\Magento\Catalog\Model\Product $product)
                     $link = $this->getProductLinkFactory()->create();
                     $link->setSku($product->getSku())
                         ->setLinkedProductSku($linkProduct->getSku())
-                        ->setLinkType($linkType->getName())
+                        ->setLinkType($linkType)
                         ->setPosition(isset($linkData['position']) ? (int)$linkData['position'] : 0);
                     $productLinks[] = $link;
                 }