Fix stream respone error for naive query mode

lightrag/operate.py

@@ -2011,9 +2011,10 @@ async def naive_query(
     response = await use_model_func(
         query,
         system_prompt=sys_prompt,
+        stream=query_param.stream,
     )
 
-    if len(response) > len(sys_prompt):
+    if isinstance(response, str) and len(response) > len(sys_prompt):
         response = (
             response[len(sys_prompt) :]
             .replace(sys_prompt, "")