forked from espressif/esp-mqtt
Some cloud server (e.g. exosite) takes empty username with password. When password is set without username, the current esp-mqtt implementation will ignore the username and only set password. This violates MQTT-3.1.2-22 [1]. To address this issue, send zero length username if password is set without username. [1] MQTT-3.1.2-22: If the User Name Flag is set to 0 then the Password Flag MUST be set to 0. Signed-off-by: Axel Lin <axel.lin@ingics.com>