Description:
------------
FilterIterator doesn't delegate count through count() array function.
It's ok if called as a method.

It affects all PHP versions: http://3v4l.org/jKOgZ

Test script:
---------------
<?php

class MyFilter extends FilterIterator
{
    public function accept()
    {
        return true;
    }
}

$it = new ArrayIterator(array(1, 2, 3));
$fi = new MyFilter($it);

var_dump($it->count());
var_dump($fi->count());

var_dump(count($it));
var_dump(count($fi));


Expected result:
----------------
int(3)
int(3)
int(3)
int(3)


Actual result:
--------------
int(3)
int(3)
int(3)
int(1)