do not popup if we have fake Base64 strings

shadowsocks-csharp/Controller/ShadowsocksController.cs

@@ -165,7 +165,7 @@ namespace Shadowsocks.Controller
             {
                 if (ssURL.IsNullOrEmpty() || ssURL.IsWhiteSpace()) return false;
                 var servers = Server.GetServers(ssURL);
-                if (servers == null) return false;
+                if (servers == null || servers.Count == 0) return false;
                 foreach (var server in servers)
                 {
                     _config.configs.Add(server);