use a new thread safe map

pkg/chunk/download.go

@@ -112,7 +112,6 @@ func (d *Downloader) downloadFromAPI(request *Request, buffer []byte, delay int6
 	downloadURL := resp.Download
 	req, err := http.NewRequest("GET", downloadURL, nil)
 	if nil != err {
-		d.log.Debugf("request init error: %v", err)
 		return fmt.Errorf("could not create request object %s %s from API", request.file.Path, request.file.Link)
 	}
 	req.Header.Add("Range", fmt.Sprintf("bytes=%v-%v", request.offsetStart, request.offsetEnd-1))