in_mqtt: fix ping response
in_mqtt: fix ping response

A ping response has no payload, but it was encoded with a payload length
of 2, confusing many MQTT clients and causing connection timeouts/drops.

Signed-off-by: Jan Willem Janssen <a82ab7284400cad371589e51b5fb02a7a4e51d94@lxtreme.nl>

nokute78/fluent-bit,nokute78/fluent-bit,fluent/fluent-bit,fluent/fluent-bit,fluent/fluent-bit,fluent/fluent-bit,nokute78/fluent-bit,nokute78/fluent-bit,fluent/fluent-bit,fluent/fluent-bit,nokute78/fluent-bit,fluent/fluent-bit,fluent/fluent-bit,nokute78/fluent-bit,fluent/fluent-bit,nokute78/fluent-bit,nokute78/fluent-bit,nokute78/fluent-bit,nokute78/fluent-bit,nokute78/fluent-bit,fluent/fluent-bit,fluent/fluent-bit,nokute78/fluent-bit,fluent/fluent-bit