fixes crashes

v2rayN/v2rayN/Forms/MainForm.cs

@@ -413,6 +413,7 @@ namespace v2rayN.Forms
                 {
                     autoLatencyRefreshTask = Task.Run(async delegate
                     {
+                        if (!this.IsHandleCreated) return; // the GUI app is exiting.
                         await Task.Delay(2000);
                         this.Invoke((MethodInvoker)(delegate
                         {

v2rayN/v2rayN/Handler/V2rayHandler.cs

@@ -303,6 +303,7 @@ namespace v2rayN.Handler
         {
             try
             {
+                if (p.HasExited) return;
                 p.CloseMainWindow();
                 p.WaitForExit(100);
                 if (!p.HasExited)

v2rayN/v2rayN/HttpProxyHandler/PrivoxyHandler.cs

@@ -138,6 +138,7 @@ namespace v2rayN.HttpProxyHandler
         {
             try
             {
+                if (p.HasExited) return; // someting, while the GUI app is exiting.
                 p.CloseMainWindow();
                 p.WaitForExit(100);
                 if (!p.HasExited)