Potential NPE in QuorumCnxManager

Findbugs flagged this, notice that we are checking for null after using the reference.

if (senderWorkerMap.get(s.socket().getInetAddress()) != null)

{ senderWorkerMap.get(s.socket().getInetAddress()).finish(); }

/*

• Start new worker thread with a clean state.
  */
  if (s != null) {