fixed no response crash

main.go

@@ -141,6 +141,12 @@ func (m UploadManager) pingWorker() error {
 				return err
 			}
 
+			if stats == nil {
+				log.Warningf("ping to %s failed: %v", conf.Host, "no response")
+				time.Sleep(time.Duration(conf.Interval) * time.Minute)
+				continue
+			}
+
 			log.Infof("ping %s over threshold detected, starting extended pings...", stats.AvgRtt)
 			for stats.AvgRtt.Milliseconds() >= conf.ThrottlePingThreshold {
 				stats, err = doPing(conf.Host, conf.ConformationPPP, time.Second)