https://github.com/ImageMagick/ImageMagick/issues/501
static OPJ_SIZE_T JP2ReadHandler(void *buffer,OPJ_SIZE_T length,void *context)
{
  Image
    *image;

  ssize_t
    count;

  image=(Image *) context;
  count=ReadBlob(image,(ssize_t) length,(unsigned char *) buffer);
  if (count == 0)
    return((OPJ_SIZE_T) -1);
  return((OPJ_SIZE_T) count);
}

static OPJ_SIZE_T JP2ReadHandler(void *buffer,OPJ_SIZE_T length,void *context)
{
  Image
    *image;

  ssize_t
    count;

  image=(Image *) context;
  count=ReadBlob(image,(ssize_t) length,(unsigned char *) buffer);
  if (count == 0)
    return((OPJ_SIZE_T) -1);
  return((OPJ_SIZE_T) count);
}
