message: Catch exception from boost::iostreams
  Summary: Okay, for some reason, the great boost throws an exception even in `open` unlike `std::fstream`. So the checking code with `is_open` didn't get executed. This made me hard to understand what file was missing. Fixed it.
diff: @@ -838,8 +838,9 @@ bool load_jar_file(const char* location,
  Scope* classes,
  attribute_hook_t attr_hook) {
  boost::iostreams::mapped_file file;
  + try {
  file.open(location, boost::iostreams::mapped_file::readonly);
  - if (!file.is_open()) {
  + } catch (const std::exception& e) {
  fprintf(stderr, "error: cannot open jar file: %s\n", location);
  return false;
  }
  