@cascade and _uid_ don't work together

[MichaelJCompton]

A query with _uid_ and @cascade doesn't return anything

e.g. the follow works fine without @cascade or without _uid_

{
	actor(func: eq(name@en, "Tom Hanks")) @cascade {
		actor.film {
			performance.film {
				~director.film {
        	_uid_
          name@en
				}
			 }
		}
	}
}

[pawanrawal]

Merged fix to master.