Fixed startup racing issue

Emby.Dlna/Main/DlnaEntryPoint.cs

@@ -228,7 +228,10 @@ namespace Emby.Dlna.Main
         {
             try
             {
-                ((DeviceDiscovery)_deviceDiscovery).Start(communicationsServer);
+                if (communicationsServer != null)
+                {
+                    ((DeviceDiscovery)_deviceDiscovery).Start(communicationsServer);
+                }
             }
             catch (Exception ex)
             {