StoreObject will mutate passed object if without fetch is set

When doing the operation:

```
T object = ...
bucket.store(object).withoutFetch().returnBody(true).withMutator(myMutator).execute();
```

The mutator will modify the passed object which per user's needs it could come up from an in-memory cache so there is no need to fetch BUT it needs to be passed to the mutation to do its job on that object.