Fix a file name parsing error

go/weed/volume.go

@@ -9,6 +9,7 @@ import (
 	"mime"
 	"net/http"
 	"os"
+	"path/filepath"
 	"runtime"
 	"strconv"
 	"strings"
@@ -268,7 +269,7 @@ func parseURLPath(path string) (vid, fid, filename, ext string) {
 	if strings.Count(path, "/") == 3 {
 		parts := strings.Split(path, "/")
 		vid, fid, filename = parts[1], parts[2], parts[3]
-		ext = filename[strings.LastIndex(filename, "."):]
+		ext = filepath.Ext(filename)
 	} else {
 		sepIndex := strings.LastIndex(path, "/")
 		commaIndex := strings.LastIndex(path[sepIndex:], ",")