Change to accept delay_sec as 0 sec

[kawasin73]

It is impossible to set 0 DelaySeconds (Execute Immediately) for SendMessage at Publisher.publish() because delay_sec or 1 is recognized as 1 when delay_sec == 0.

DelaySeconds for send_message() does not accept None but only int. It is reasonable to check delay_sec is None or not by or. But i think the fallback value should be 0.