Description:
------------
If you wrap a RecursiveArrayIterator in a RecursiveIteratorIterator and iterate past the end of the array, PHP crashes.

Reproduce code:
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<?php
$i = new RecursiveIteratorIterator(new RecursiveArrayIterator(array()));
$i->next();
var_dump($i->current());
?>

Expected result:
----------------
NULL

Actual result:
--------------
Segmentation fault (core dumped)