fix validation error double fetmeeting

fet2020/posts/models.py

@@ -306,7 +306,7 @@ class Event(Post):
             raise ValidationError(_("Das Datum des Events fehlt."))
         if self.event_end and self.event_end < self.event_start:
             raise ValidationError(_("Das Ende des Events liegt vor dem Beginn."))
-
+        super().clean()
     def save(self, *args, **kwargs):
         if not self.post_type:
             self.post_type = "E"
@@ -365,7 +365,11 @@ class FetMeeting(Event):
 #        return protocol_key
  
         
-
+    def clean(self):
+        super().clean()
+        if not self.slug:
+            self.slug = self.__get_slug()
+      
     def save(self, *args, **kwargs):
         self.title = "Fachschaftssitzung"
         if not self.slug: