fix: initialize result variable in generate_description_embedding

The result variable is only assigned inside the semantic_search.enabled
and len(new_description) > 0 conditions. If either is false, the return
statement references an undefined variable, raising UnboundLocalError.

Initialize result = None before the conditional block.

frigate/api/event.py

@@ -1639,6 +1639,7 @@ def generate_description_embedding(
     body: EventsDescriptionBody,
 ):
     new_description = body.description
+    result = None
 
     # If semantic search is enabled, update the index
     if request.app.frigate_config.semantic_search.enabled: