fix invalid memory address or nil pointer dereference on filer.sync

fix https://github.com/seaweedfs/seaweedfs/issues/3826

weed/replication/sink/filersink/filer_sink.go

@@ -54,7 +54,6 @@ func (fs *FilerSink) IsIncremental() bool {
 func (fs *FilerSink) Initialize(configuration util.Configuration, prefix string) error {
 	fs.isIncremental = configuration.GetBool(prefix + "is_incremental")
 	fs.dataCenter = configuration.GetString(prefix + "dataCenter")
-	fs.executor = util.NewLimitedConcurrentExecutor(32)
 	return fs.DoInitialize(
 		"",
 		configuration.GetString(prefix+"grpcAddress"),
@@ -85,6 +84,7 @@ func (fs *FilerSink) DoInitialize(address, grpcAddress string, dir string,
 	fs.diskType = diskType
 	fs.grpcDialOption = grpcDialOption
 	fs.writeChunkByFiler = writeChunkByFiler
+	fs.executor = util.NewLimitedConcurrentExecutor(32)
 	return nil
 }