Avoid overflow in ljpeg_start().
unsigned CLASS get4()
{
  uchar str[4] = { 0xff,0xff,0xff,0xff };
  fread (str, 1, 4, ifp);
  return sget4(str);
}

unsigned CLASS get4()
{
  uchar str[4] = { 0xff,0xff,0xff,0xff };
  fread (str, 1, 4, ifp);
  return sget4(str);
}
