MediaCollection.add_episde: detect change & act accordingly

- only apply changes if episode is new or new data is given
- flush only if changes are given
- return link only on changes / creation

server/entertainment_decider/models.py

@@ -777,15 +777,21 @@ class MediaCollection(db.Entity, Tagable):
         media: MediaElement,
         season: int = 0,
         episode: int = 0,
-    ) -> MediaCollectionLink:
+    ) -> Optional[MediaCollectionLink]:
         link: MediaCollectionLink = MediaCollectionLink.get(
             collection=self, element=media
         )
+        change = False
         if link is None:
+            change = True
             link = MediaCollectionLink(collection=self, element=media)
+        if (link.season, link.episode) != (season, episode):
+            change = True
             link.season, link.episode = season, episode
+        if change:
             orm.flush()
             return link
+        return None
 
     def add_single_uri(self, uri: str) -> bool:
         mapping: CollectionUriMapping = CollectionUriMapping.get(uri=uri)