fix: revert back to only passing the network id if its set, due to dart bug being fixed

protocol/handshake_open.go

@@ -56,11 +56,12 @@ func (h HandshakeOpen) EncodeMsgpack(enc *msgpack.Encoder) error {
 		return err
 	}
 
+	if h.networkId != "" {
 		err = enc.EncodeString(h.networkId)
 		if err != nil {
 			return err
 		}
-
+	}
 	return nil
 }