Fix case when SerializableClosure uses as class property

[Dry7]

This pull request fix the case when SerializableClosure is used as one of the class properties. At the moment, it is SerializableClosure replaced by a Closure. This behavior was the cause of this issue https://github.com/laravel/serializable-closure/issues/106

[ralphschindler]

I've recently run into this problem as well when mixing Batches and Jobs inside a chain()