Fix config selection

User wants to use that server after selected it in the ConfigForm. If user deletes
the server in use, we can't find its index, then the previous logic will revert to
index 0, which is not expected behaviour.

Since we handled 'ServersListBox.SelectedIndex' in various event handlers, we can
trust it all the time.

Signed-off-by: Syrone Wong <wong.syrone@gmail.com>

shadowsocks-csharp/View/ConfigForm.cs

@@ -230,7 +230,6 @@ namespace Shadowsocks.View
 
         private void OKButton_Click(object sender, EventArgs e)
         {
-            Server server = controller.GetCurrentServer();
             if (!SaveOldSelectedServer())
             {
                 return;
@@ -241,7 +240,10 @@ namespace Shadowsocks.View
                 return;
             }
             controller.SaveServers(_modifiedConfiguration.configs, _modifiedConfiguration.localPort);
-            controller.SelectServerIndex(_modifiedConfiguration.configs.IndexOf(server));
+            // SelectedIndex remains valid
+            // We handled this in event handlers, e.g. Add/DeleteButton, SelectedIndexChanged
+            // and move operations
+            controller.SelectServerIndex(ServersListBox.SelectedIndex);
             this.Close();
         }