On ne met pas à jour la localisation exacte si elle n'est pas pertinente

Fix #398

src/agenda_culturel/models.py

@@ -2256,6 +2256,8 @@ class Event(models.Model):
                 continue
             if attr == "start_day" and other.has_invalid_start_date():
                 continue
+            if attr == "exact_location" and other.exact_location is None:
+                continue
             setattr(self, attr, getattr(other, attr))
 
         # adjust modified date if required