Incorrect handling of DISCONNECT packet

[NickFoubert]

I believe the handling of DISCONNECT (at least for MQTT 5) isn't correct:

https://github.com/eclipse/paho.mqtt.python/blob/d45de3737879cfe7a6acc361631fa5cb1ef584bb/src/paho/mqtt/client.py#L4021C1-L4022C1

I'm using paho as a test client and it doesn't seem to be correctly handling a DISCONNECT packet with a non-zero reason code and zero length properties (i.e. Remaining_Length = 2).

[abeaum]

I have also come across the same issue, which appears also to be dependent on the MQTT broker.

The DISCONNECT reason codes can be extracted by paho-mqtt when using hivemq as a broker (because hivemq DISCONNECT packet has a length > 2 bytes), but it doesn't extract the reason code when I use mosquitto.