message: ftp: static_assert fix for older compilers
diff: @@ -173,7 +173,9 @@ private:
  Ftp::result_callback_t _curr_op_result_callback{};
  // _curr_op_progress_callback is used for download_callback_t as well as upload_callback_t
  - static_assert(std::is_same<Ftp::download_callback_t, Ftp::upload_callback_t>::value);
  + static_assert(
  + std::is_same<Ftp::download_callback_t, Ftp::upload_callback_t>::value,
  + "callback types don't match");
  Ftp::download_callback_t _curr_op_progress_callback{};
  Ftp::list_directory_callback_t _curr_dir_items_result_callback{};
  