Description:
------------
PDOStatement::fetchAll(PDO::FETCH_FUNC,function() {}) fails not being able to recognize Closure as valid callback.

Reproduce code:
---------------
<?php
 $db = new PDO('sqlite::memory:');
 $db->exec('CREATE TABLE `a` ( `id` INTEGER )');

 $st = $db->query('SELECT * FROM `a`');
 $st->fetchAll(PDO::FETCH_FUNC,function() {});
?>


Expected result:
----------------
No error

Actual result:
--------------
Warning: PDOStatement::fetchAll() [pdostatement.fetchall]: SQLSTATE[HY000]: General error: user-supplied function must be a valid callback in ... on line 6