allow Kekno to run with sv_running not returning anything :upside_down:

make sure script plugins output correct errors instead of being swallowed
prevent webfront error when webfront tab is left open on a server no longer being modified

WebfrontCore/Controllers/ServerController.cs

@@ -21,7 +21,7 @@ namespace WebfrontCore.Controllers
 
             if (s == null)
             {
-                return View("Error", "Invalid server!");
+                return NotFound();
             }
 
             var serverInfo = new ServerInfo()