filer: fix http status 206 setting

fix https://github.com/chrislusf/seaweedfs/issues/1753

weed/server/filer_server_handlers_read.go

@@ -159,10 +159,10 @@ func (fs *FilerServer) GetOrHeadHandler(w http.ResponseWriter, r *http.Request,
 	}
 
 	processRangeRequest(r, w, totalSize, mimeType, func(writer io.Writer, offset int64, size int64, httpStatusCode int) error {
-		if offset+size <= int64(len(entry.Content)) {
 		if httpStatusCode != 0 {
 			w.WriteHeader(httpStatusCode)
 		}
+		if offset+size <= int64(len(entry.Content)) {
 			_, err := writer.Write(entry.Content[offset : offset+size])
 			return err
 		}