Description:
------------
Not sure if this a bug or a feature, but when applying a fixed reference to a member of the iterator returned by the children() method in a foreach construct, it gets stuck in an infinite loop.

Reproduce code:
---------------
<?php

$xml = '<parent><element /><child /></parent>';
$xmldoc = simplexml_load_string($xml);
$elements = $xmldoc->children();

foreach ($elements as $element) {
   $elements[0];
}

?>

Expected result:
----------------
Finished after a couple of seconds at most.

Actual result:
--------------
Infinite loop.