Add system data integrity check

api/savedata.go

@@ -120,6 +120,11 @@ func (s *Server) HandleSavedataUpdate(w http.ResponseWriter, r *http.Request) {
 			return
 		}
 
+		if system.TrainerId == 0 && system.SecretId == 0 {
+			http.Error(w, "invalid system data", http.StatusInternalServerError)
+			return
+		}
+
 		var gobBuffer bytes.Buffer
 		err = gob.NewEncoder(&gobBuffer).Encode(system)
 		if err != nil {