panic: send closed channel - incomingMessages

[Allenxuxu]

go-nsq/consumer.go

Line 767 in 2a2babe

err := r.ConnectToNSQD(addr)

In extreme case, before it is successful, consumer has been stop.
It may lead to panic. Because of

func (r *Consumer) stopHandlers() {
	r.stopHandler.Do(func() {
		r.log(LogLevelInfo, "stopping handlers")
		close(r.incomingMessages)
	})
}

[mreiferson]

see #326