Parse cookie values "{}" & "[]" as array

Cookies set to values  "{}" & "[]" directly in a HTTP Client (e.g. a browser) are not being parsed as PHP arrays. I think we should only discard the cases [where](http://php.net/manual/en/function.json-decode.php#refsect1-function.json-decode-returnvalues) "..the json cannot be decoded or if the encoded data is deeper than the recursion limit."