Description:
------------
The default value for RegexIterator's pregFlags is supposed to be zero, but it is NULL. This is inconsistent.

Test script:
---------------
http://3v4l.org/cRmui

<?php

$arr = new ArrayIterator(array());
$regex = new RegexIterator($arr, '/^test/');
var_dump($regex->getMode(),
         $regex->getFlags(),
         $regex->getPregFlags()
        );

Expected result:
----------------
int(0)
int(0)
int(0) 

Actual result:
--------------
int(0)
int(0)
NULL