Json: workaroud for PHP fatal error

PHP function `json_decode` has a nasty bug which lead to **fatal error** if key starts with a NULL byte. Simple workaround for this is to pass `true` as the second parameter. Any tips how to solve this issue in `Nette\Utils\Json`?

<del>This pull contains only failing test for now.</del> 
This is faster '#(?<!\\\\)"\\\\u0000(?:[^"\\\\]|\\\\.)*+"\s*+:#'