special case fix for streadway/amqp/issues/161
special case fix for streadway/amqp/issues/161

fixes the situation in which both server and client have decided the
max frame size is 0 by detecting it and special casing the size to be
the length of what you're trying to publish, keeping the `Setting to 0
means "unlimited"` semantics from www.rabbitmq.com/configure.html

ChannelMeter/amqp,TeamFairmont/amqp,streadway/amqp,TeamFairmont/amqp,ChannelMeter/amqp,streadway/amqp