func readBlockAt(reader io.ReadSeeker, offset int64) (fileBlock, error) {
	var block fileBlock
	_, err := reader.Seek(offset, os.SEEK_SET)
	if err != nil {
		return block, err
	}
	return block, binary.Read(reader, binary.LittleEndian, &block)
}
func readBlockAt(reader io.ReadSeeker, offset int64) (fileBlock, error) {
	var block fileBlock
	_, err := reader.Seek(offset, os.SEEK_SET)
	if err != nil {
		return block, err
	}
	return block, binary.Read(reader, binary.LittleEndian, &block)
}
// Read meta-info at specified place