Description:
------------
When running the below in PHP 7.1.0, the foreach loop hangs the script, and my CPU goes to 100% utilization.

If &$value is changed to $value, then it runs cleanly.


Test script:
---------------
<?php
$a = 'aaa';

foreach ($a['bbb'] as &$value)
{
	echo 'loop';
}

unset($value);

echo 'done';


Expected result:
----------------
Warning: Illegal string offset 'bbb' in /tmp/test.php on line 4

Warning: Invalid argument supplied for foreach() in /tmp/test.php on line 4
done


Actual result:
--------------
Warning: Illegal string offset 'bbb' in /tmp/test.php on line 4

then it hangs