Don't crash when adding a NIC to a PC/server (Justin)

EduNetworkBuilder/DeviceConfig.cs

@@ -357,7 +357,7 @@ namespace EduNetworkBuilder
                         tnic = ndCLonedItem.AddNic(WhatToAdd[cbQuestions.SelectedIndex]);
                     }
                 }
-                if(tnet != null)
+                if(tnet != null && tnic != null)
                     tnet.RegisterNICAdded(ndCLonedItem.hostname, tnic.NicName());
             }
             UpdateForm();