Description:
------------
When I want to push an element in an array item of SplFixedArray, I get an error 
notice.
Tested on 5.4.6-1ubuntu1.2.

Test script:
---------------
$a = new SplFixedArray(1);
$a[0] = array();

array_push($a[0], 'test');

Actual result:
--------------
Notice: Indirect modification of overloaded element of SplFixedArray has no 
effect