Empty lora payload sent on port 0

[jpmeijers]

If I send a lorawan message with an empty payload, even if I specify a port, the message is sent on port 0. This is invalid, as port 0 is reserved for mac commands.

[jpmeijers]

I believe the issue is related to this block of code:

ArduinoCore-stm32l0/system/STM32L0xx/Source/LoRa/Mac/LoRaMac.c

Lines 2308 to 2310 in b1cf1cd

	if( ( payload != NULL ) && ( LoRaMacTxPayloadLen > 0 ) )
	{
	LoRaMacBuffer[pktHeaderLen++] = framePort;

The port is only added to the payload if the payload is > 0, but that should be >=0.