MAGETWO-91701: Newsletter subscription is not correctly updated when user is registered on 2 stores

- Adding additional checking for guest customers

Author: vprohorov

app/code/Magento/Newsletter/Model/ResourceModel/Subscriber.php

@@ -48,6 +48,13 @@ class Subscriber extends \Magento\Framework\Model\ResourceModel\Db\AbstractDb
      */
     protected $mathRandom;
 
+    /**
+     * Guest customer id
+     *
+     * @var int
+     */
+    private $guestCustomerId = 0;
+
     /**
      * Construct
      *
@@ -136,22 +143,24 @@ public function loadByCustomerData(\Magento\Customer\Api\Data\CustomerInterface
             return $result;
         }
 
-        $select = $this->connection
-            ->select()
-            ->from($this->getMainTable())
-            ->where('subscriber_email=:subscriber_email and store_id=:store_id');
-
-        $result = $this->connection
-            ->fetchRow(
-                $select,
-                [
-                    'subscriber_email' => $customer->getEmail(),
-                    'store_id' => $customer->getStoreId()
-                ]
-            );
-
-        if ($result) {
-            return $result;
+        if ($customer->getId() === $this->guestCustomerId) {
+            $select = $this->connection
+                ->select()
+                ->from($this->getMainTable())
+                ->where('subscriber_email=:subscriber_email and store_id=:store_id');
+
+            $result = $this->connection
+                ->fetchRow(
+                    $select,
+                    [
+                        'subscriber_email' => $customer->getEmail(),
+                        'store_id' => $customer->getStoreId()
+                    ]
+                );
+
+            if ($result) {
+                return $result;
+            }
         }
 
         return [];