fix ec shard spreading error

weed/server/volume_grpc_erasure_coding.go

@@ -111,7 +111,7 @@ func (vs *VolumeServer) VolumeEcShardsCopy(ctx context.Context, req *volume_serv
 	}
 
 	dataBaseFileName := storage.VolumeFileName(location.Directory, req.Collection, int(req.VolumeId))
-	indexBaseFileName := storage.VolumeFileName(location.Directory, req.Collection, int(req.VolumeId))
+	indexBaseFileName := storage.VolumeFileName(location.IdxDirectory, req.Collection, int(req.VolumeId))
 
 	err := operation.WithVolumeServerClient(req.SourceDataNode, vs.grpcDialOption, func(client volume_server_pb.VolumeServerClient) error {