提交代码，解决用户图像更新问题

Signed-off-by: zouap <zouap@pcl.ac.cn>

models/user.go

@@ -497,7 +497,7 @@ func (u *User) RealSizedAvatarLink(size int) string {
 // service.
 func (u *User) RelAvatarLink() string {
 	append := ""
-	if u.Avatar != ""{
+	if u.UseCustomAvatar {
 		append = "?" + fmt.Sprint(rand.Intn(100))
 	}
 	return u.SizedRelAvatarLink(base.DefaultAvatarSize) + append