Fix d'un bug possible quand on créé un groupe dupliqué

src/agenda_culturel/models.py

@@ -1370,9 +1370,10 @@ class Event(models.Model):
             # otherwise merge existing groups
             group = DuplicatedEvents.merge_groups(groups)
 
+        group.save()
+
         if force_non_fixed:
             group.representative = None
-        group.save()
 
         # set the possibly duplicated group for the current object
         self.other_versions = group