Handle case where kafka returns 0 partitions (#16)

async/kafka/kafka.go

@@ -158,7 +158,12 @@ func (c *consumer) Consume(ctx context.Context) (<-chan async.Message, <-chan er
 	if err != nil {
 		return nil, nil, errors.Wrap(err, "failed to get partitions")
 	}
-	log.Infof("consuming messages for topic '%s'", c.topic)
+	// When kafka cluster is not fully initialized, we may get 0 partions.
+	if len(pcs) == 0 {
+		return nil, nil, errors.New("got 0 partitions")
+	}
+
+	log.Infof("consuming messages for topic '%s' from %d partitions", c.topic, len(pcs))
 	chMsg := make(chan async.Message, c.buffer)
 	chErr := make(chan error, c.buffer)