[skip ci]Add comment for rocksmq reader (#12897)

Signed-off-by: fishpenguin <kun.yu@zilliz.com>

internal/util/rocksmq/client/rocksmq/reader_impl.go

@@ -69,6 +69,7 @@ func (r *reader) Next(ctx context.Context) (Message, error) {
 	return msg, nil
 }
 
+// HasNext check if there is a message available to read
 func (r *reader) HasNext() bool {
 	return r.c.server.HasNext(r.topic, r.name, r.startMessageIDInclusive)
 }