//
// The Header.Size does not reflect the size of any extended headers used.
// Thus, this function will read from the raw io.Reader to fetch extra headers.
// This method mutates blk in the process.
func (tr *Reader) readOldGNUSparseMap(hdr *Header, blk *block) (sparseDatas, error) {
	// Make sure that the input format is GNU.
	// Unfortunately, the STAR format also has a sparse header format that uses