prevent nil dereference on CompareAndSwap errors

masterelection/masterelection.go

@@ -132,6 +132,7 @@ func (m *MasterElection) runMaster(index uint64, stop chan bool) {
 					m.Log.Println("too many errors, lost lock")
 					return
 				}
+				continue
 			}
 			index = resp.EtcdIndex
 			lastUpdate = t