Merge pull request #3 from ziXiong/main

Fix null URL ETag for better compatibility

Author: paul-norman

download.go

@@ -112,7 +112,7 @@ func downloadFile(filePath string, url string) (bool, error) {
 	fmt.Println("downloading Etag: " + url)
 	newEtag := getEtag(url)
 
-	if newEtag != "" && currentEtag != newEtag {
+	if newEtag == "" || currentEtag != newEtag {
 		fileWriteSmall(etagFilePath, newEtag)
 
 		fmt.Println("downloading data file: " + url)
@@ -150,4 +150,4 @@ func downloadSelect(name string, downloads []Download, missing []string) []Downl
 	}
 
 	return downloads
-}
+}