code: func (t *Torrent) forReaderOffsetPieces(f func(begin, end pieceIndex) (more bool)) (all bool) {
  	for r := range t.readers {
  		p := r.pieces
  		if p.begin >= p.end {
  			continue
  		}
  		if !f(p.begin, p.end) {
  			return false
  		}
  	}
  	return true
  }
docs: // Returns true if all iterations complete without breaking. Returns the read
  // regions for all readers. The reader regions should not be merged as some
  // callers depend on this method to enumerate readers.