consumer: Deal with case where no connections during backoff.
consumer: Deal with case where no connections during backoff.

This fixes the following scenario:
1. Consumer is connected to one NSQD host using ConnectToNSQD.
2. Consumer receives message and handler returns an error.
3. Consumer backs off.
4. DisconnectFromNSQD called before backoff closure wakes up.
5. Backoff closure wakes up, sees no connections, returns.
6. Consumer connects to NSQD host using ConnectToNSQD.
7. backoffCounter still > 0 so never sends RDY count (in
maybeUpdateRDY).
8. Consumer is now stuck and never sends RDY > 0.

jmptrader/go-nsq,glycerine/go-nsq,jmptrader/go-nsq,bitly/go-nsq,server-nado/go-nsq,yepengxj/go-nsq,mreiferson/go-nsq,mreiferson/go-nsq,DanielHeckrath/go-nsq,grepory/go-nsq,absolute8511/go-nsq,bitly/go-nsq,yepengxj/go-nsq,deepglint/go-nsq,fayep/go-nsq,nsqio/go-nsq,judwhite/go-nsq,absolute8511/go-nsq,deepglint/go-nsq,nsqio/go-nsq,fayep/go-nsq,grepory/go-nsq,glycerine/go-nsq,judwhite/go-nsq,DanielHeckrath/go-nsq,server-nado/go-nsq