Fix non unique messages shown when adding items to cart

Author: volodyaprokopchuk

app/code/Magento/Quote/Model/Quote.php

@@ -1619,10 +1619,11 @@ public function addProduct(
 
             // collect errors instead of throwing first one
             if ($item->getHasError()) {
-                $message = $item->getMessage();
-                if (!in_array($message, $errors)) {
-                    // filter duplicate messages
-                    $errors[] = $message;
+                foreach ($item->getMessage(false) as $message) {
+                    if (!in_array($message, $errors)) {
+                        // filter duplicate messages
+                        $errors[] = $message;
+                    }
                 }
             }
         }