Description:
------------
Function array dereferencing does not work for splFixedArray.

Test script:
---------------
<?php
$a = new splFixedArray(5);
$a[0] = array(1, 2, 3);
$a[0][0] = 10;
?>

Expected result:
----------------
No error.

Actual result:
--------------
"Notice: Indirect modification of overloaded element of SplFixedArray has no effect in [filename] on line 4"