Description:
------------
When accessing a string by character offset php doesnt trigger error when going out of bounds of the string or accessing a non existing element.

Reproduce code:
---------------
<?php
$moo="asd";
var_dump($moo[444]);
var_dump($moo['cow']);
?>



Expected result:
----------------
Return false or null since the offset or index is not defined.


Actual result:
--------------
Notice: Uninitialized string offset:  444 in /home/tachu/.thunderbird/xs4vamjr.default/moo on line 3
string(0) ""
string(1) "a"