Fix: "AttributeError(\"'list' object has no attribute 'get'\")" (#12518)

### What problem does this PR solve?
https://github.com/infiniflow/ragflow/issues/12515

### Type of change

- [x] Bug Fix (non-breaking change which fixes an issue)

api/apps/sdk/session.py

@@ -425,7 +425,7 @@ async def chat_completion_openai_like(tenant_id, chat_id):
             ],
         }
         if need_reference:
-            response["choices"][0]["message"]["reference"] = chunks_format(answer.get("reference", []))
+            response["choices"][0]["message"]["reference"] = chunks_format(answer.get("reference", {}))
 
         return jsonify(response)