Fix adding values to variable collection

Changed select fields in joined variable value table in Magento\Variable\Model\ResourceModel\Variable\Collection#addValuesToResult() method to match DB schema

Author: mszydlo

app/code/Magento/Variable/Model/ResourceModel/Variable/Collection.php

@@ -62,7 +62,7 @@ public function addValuesToResult()
         $this->getSelect()->join(
             ['value_table' => $this->getTable('variable_value')],
             'value_table.variable_id = main_table.variable_id',
-            ['value_table.value']
+            ['value_table.plain_value', 'value_table.html_value']
         );
         $this->addFieldToFilter('value_table.store_id', ['eq' => $this->getStoreId()]);
         return $this;