do not preview prompt at error return from chat response

app.py

@@ -197,7 +197,7 @@ def chat_response(user_msg, chat_history, system_prompt,
         yield history, debug + prompt_debug
     except Exception as e:
         history[-1]['content'] = f"Error: {e}"
-        yield history, debug + prompt_debug
+        yield history, debug
     finally:
         gc.collect()