Stop the PACServer when controller stop

shadowsocks-csharp/Controller/ShadowsocksController.cs

@@ -128,6 +128,11 @@ namespace Shadowsocks.Controller
             {
                 polipoRunner.Stop();
             }
+            if (pacServer != null)
+            {
+                pacServer.Stop();
+                pacServer = null;
+            }
             if (_config.enabled)
             {
                 SystemProxy.Disable();