[fixes] Remove error from udp semtech when no downlink is sent
[fixes] Remove error from udp semtech when no downlink is sent

jvanmalder/ttn,mgranberry/ttn,TheThingsNetwork/ttn,mgranberry/ttn,TheThingsNetwork/ttn,LoRaWanSoFa/ttn,jvanmalder/ttn,jvanmalder/ttn,mgranberry/ttn,TheThingsNetwork/ttn,LoRaWanSoFa/ttn