BUG:panic about conSyncDAGHandler

Author: lochjin

p2p/synch/syncdag.go

@@ -61,6 +61,10 @@ func (s *Sync) conSyncDAGHandler(ctx context.Context, msg interface{}, stream li
 
 	gs := pe.GraphState()
 	blocks, point := s.PeerSync().dagSync.CalcSyncBlocks(gs, []*hash.Hash{changePBHashToHash(m.SyncPoint), changePBHashToHash(m.Start)}, meerdag.ContinueMode, MaxBlockLocatorsPerMsg)
+	if point == nil || len(blocks) <= 0 {
+		err := fmt.Errorf("CalcSyncBlocks error by ContinueMode: point=%s start=%s", m.SyncPoint.String(), m.Start.String())
+		return ErrMessage(err)
+	}
 	pe.UpdateSyncPoint(point)
 	sd := &pb.SubDAG{SyncPoint: &pb.Hash{Hash: point.Bytes()}, GraphState: s.getGraphState(), Blocks: changeHashsToPBHashs(blocks)}