fix(filer.sync): offset may be set to 0 (#3451)

* fix(filer.sync): initializing the offset is related to the path

* fix(filer.sync): the offset maybe to be set to 0.

Co-authored-by: zhihao.qu <zhihao.qu@ly.com>

weed/command/filer_sync.go

@@ -259,6 +259,9 @@ func doSubscribeFilerMetaChanges(clientId int32, clientEpoch int32, grpcDialOpti
 		processor.AddSyncJob(resp)
 		return nil
 	}, 3*time.Second, func(counter int64, lastTsNs int64) error {
+		if processor.processedTsWatermark == 0 {
+			return nil
+		}
 		// use processor.processedTsWatermark instead of the lastTsNs from the most recent job
 		now := time.Now().UnixNano()
 		glog.V(0).Infof("sync %s to %s progressed to %v %0.2f/sec", sourceFiler, targetFiler, time.Unix(0, processor.processedTsWatermark), float64(counter)/(float64(now-lastLogTsNs)/1e9))