django-chunked-upload: 'user' field passed to BaseChunkedUpload causes exception

In my code I’ve extended BaseChunkedUpload without adding a user field. If the django request is authenticated, an error is thrown after injecting a user field into the attrs dict here:

https://github.com/juliomalegria/django-chunked-upload/blob/master/chunked_upload/views.py#L184

There should be an extra condition which verifies that a user field exists on self.model before injecting it into attrs.