Allow client and server negotiate on savegame format if both are patched

src/network/network_client.cpp

@@ -355,6 +355,7 @@ NetworkRecvStatus ClientNetworkGameSocketHandler::SendJoin()
 	p->Send_string(_settings_client.network.client_name); // Client name
 	p->Send_uint8 (_network_join_as);     // PlayAs
 	p->Send_uint8 (NETLANG_ANY);          // Language
+	p->Send_uint8 (citymania::GetAvailableLoadFormats());  // Compressnion formats that we can decompress
 	my_client->SendPacket(p);
 	return NETWORK_RECV_STATUS_OKAY;
 }