setTranslator(null) in method throws TypeError

Version: dev-master

### Bug Description
Argument 2 passed to Latte\Engine::addFilter() must be callable, null given:
https://github.com/nette/application/blob/master/src/Bridges/ApplicationLatte/Template.php#L100

when `$translator = null`

because addFilter accepts only callable, not ?callable https://github.com/nette/latte/blob/master/src/Latte/Engine.php#L232
