code: func (t *deviceDownloadState) Has(folder, file string, version protocol.Vector, index int32) bool {
  	if t == nil {
  		return false
  	}
  	t.mut.RLock()
  	f, ok := t.folders[folder]
  	t.mut.RUnlock()
  
  	if !ok {
  		return false
  	}
  
  	return f.Has(file, version, index)
  }
docs: // Has returns whether block at that specific index, and that specific version of the file
  // is currently available on the remote device for pulling from a temporary file.