Fix: vieux sondages

Les sondages archivés (`survey.old = True`) mais toujours ouverts
(`survey.suervy_open = True`) restaient accessibles. Ce n'est plus le cas

gestioncof/views.py

@@ -94,7 +94,7 @@ def logout(request):
 @login_required
 def survey(request, survey_id):
     survey = get_object_or_404(Survey, id=survey_id)
-    if not survey.survey_open:
+    if not survey.survey_open or survey.old:
         raise Http404
     success = False
     deleted = False