message: Register readers and avoid pointer arithmetic
diff: @@ -155,14 +155,16 @@ GetProjectionsFileNamesFromGgo(const TArgsInfo &args_info)
  std::vector<std::string> fileNames = names->GetFileNames();
  rtk::RegisterIOFactories();
  std::vector<size_t> idxtopop;
  + size_t i = 0;
  for (auto fn : fileNames) {
  itk::ImageIOBase::Pointer imageio = itk::ImageIOFactory::CreateImageIO(
  fn.c_str(), itk::ImageIOFactory::ReadMode);
  if (imageio.IsNull()) {
  std::cerr << "Ignoring file: " << fn << std::endl;
  - idxtopop.push_back(&fn - &fileNames[0]);
  + idxtopop.push_back(i);
  }
  + i++;
  }
  std::reverse(idxtopop.begin(), idxtopop.end());
  for (auto id : idxtopop) {
  