Fixed execute_safe. If an error occurs $result will contain 'code' fi…

…eld instead 'errno'

classes/mongo/database.php

@@ -329,7 +329,7 @@ public function execute_safe( $code, array $args = array(), $scope = array() )
     $result = $this->execute($code, $args);
     if( empty($result['ok']) )
     {
-      throw new MongoException($result['errmsg'], $result['errno']);
+      throw new MongoException($result['errmsg'], $result['code']);
     }
     return $result['retval'];
   }