Fix tbtr refit button crashing if new template window is empty.

src/tbtr_template_gui_create.cpp

@@ -244,7 +244,9 @@ public:
 				break;
 			}
 			case TCW_REFIT: {
-				ShowVehicleRefitWindow(virtual_train, INVALID_VEH_ORDER_ID, this, false, true);
+				if (virtual_train != NULL) {
+					ShowVehicleRefitWindow(virtual_train, INVALID_VEH_ORDER_ID, this, false, true);
+				}
 				break;
 			}
 		}