Fix integration error preventing coupon codes to be applied.

Author: david-fuehr

app/code/Magento/SalesRule/Model/ResourceModel/Rule/Collection.php

@@ -167,7 +167,10 @@ public function setValidationFilter(
                 $allAllowedRules = $this->getConnection()->select();
                 $allAllowedRules->union([$noCouponRules, $couponRules], \Zend_Db_Select::SQL_UNION_ALL);
 
-                $this->_select = $allAllowedRules;
+                $wrapper = $this->getConnection()->select();
+                $wrapper->from($allAllowedRules);
+
+                $this->_select = $wrapper;
             } else {
                 $this->_select = $noCouponRules;
             }