error if file couldnt be opened

File.cpp

@@ -42,6 +42,7 @@ void File::reset() {
 
   if (_file) close(_file);
   _file = open(_path.c_str(), O_RDONLY);
+  if (_file < 0) throw XmlFileException(std::string("could not open ") + _path);
   posix_fadvise(_file, 0, 0, POSIX_FADV_SEQUENTIAL);
 
   _lastBytes = read(_file, _buffer[_which], BUFFER_S);