Merge remote-tracking branch 'ogresCE/MAGETWO-44919-hhvm-libxml-error' into PR_Branch

Author: mazhalai

lib/internal/Magento/Framework/Config/Dom.php

@@ -276,6 +276,10 @@ public static function validateDomDocument(
         $schema,
         $errorFormat = self::ERROR_FORMAT_DEFAULT
     ) {
+        if (!function_exists('libxml_set_external_entity_loader')) {
+            return [];
+        }
+
         if (!self::$urnResolver) {
             self::$urnResolver = new UrnResolver();
         }