Description:
------------
Casting a decoded simple json structure into an array doesn't allow lookups by key if the key is numeric.

Test script:
---------------
$a = json_decode('{"b": {"c": {"10": "abc", "11": "def"}}}');

$aa = (array)$a->b->c;

var_dump($aa['10']);

Expected result:
----------------
string(3) "abc"

Actual result:
--------------
Notice: Undefined offset: 10 in /in/d0290 on line 7
NULL