Fix panic during error returning if Dataset\Query couldn't have found

[Tsovak]

the application panics when couldn't find a query. at this point, it returns return nil, status.Error(codes.NotFound, err.Error()). but here err is nil because 2 lines above we check that

		log.Err(err).Send()
		return nil, status.Error(codes.Internal, err.Error())
	}

just couldn't find a Dataset\Query

I just deleted panic cause (err.Error()) and added just a message