update conditional check

set response_id=None when there is a valid response_id but latest_model_request doesn't exist

Co-authored-by: Douwe Maan <[email protected]>

Author: GDaamn

pydantic_ai_slim/pydantic_ai/models/openai.py

@@ -1099,8 +1099,9 @@ def _get_response_id_and_trim(self, messages: list[ModelMessage]) -> tuple[list[
                 response_id = None
                 break
         if response_id and latest_model_request:
-            messages = [latest_model_request]
-        return messages, response_id
+            return [latest_model_request], response_id
+        else:
+            return messages, None
 
     async def _map_messages(  # noqa: C901
         self, messages: list[ModelMessage]