Description:
------------
when I use DirectoryIterator::__construct to get a new DirectoryIterator, I found it do not throw exception when "" and NULL passed as argument.

Reproduce code:
---------------
<?php
$max=mt_getrandmax();
$ar=array(1,2,3);
$ite=new RecursiveArrayIterator($ar);

$invalid=array("",new Exception,array(),$ite,$max+1,NULL,"/no/such/dir");

foreach($invalid as $p)
{
        try
        {
                $ak=new DirectoryIterator($p);
                var_dump($ak->valid());
                var_dump($ak->getPathname());
                echo "I will never come out\n";
        }catch(Exception $e)
        {
                echo "exception caught with parameter $p\n";
        }
}
?>


Expected result:
----------------
exception caught with parameter ""
exception caught with parameter Object id #2
exception caught with parameter Array
exception caught with parameter Object id #1
exception caught with parameter 2147483648
exception caught with parameter NULL
exception caught with parameter /no/such/dir


Actual result:
--------------
bool(false)
bool(false)
I will never come out
exception caught with parameter Object id #2
exception caught with parameter Array
exception caught with parameter Object id #1
exception caught with parameter 2147483648
bool(false)
bool(false)
I will never come out
exception caught with parameter /no/such/dir