[performance] Correcting invalid 0 passed by PeerDiscovery & PeerDiscoveryMonitorThread

![before - labelledchaindownloadedlocationsopenedeverythingclosed](https://cloud.githubusercontent.com/assets/5212629/4261944/380c6884-3b85-11e4-8468-e61c8d985cf5.png)
![after-peersstillwork](https://cloud.githubusercontent.com/assets/5212629/4261948/411bdc52-3b85-11e4-91a6-378aaa5da6f0.png)