fix: access control

backend/open_webui/main.py

@@ -1147,7 +1147,7 @@ async def generate_chat_completions(
     # Check if user has access to the model
     if user.role == "user":
         model_info = Models.get_model_by_id(model_id)
-        if not (
+        if model_info and not (
             user.id == model_info.user_id
             or has_access(
                 user.id, type="read", access_control=model_info.access_control