bug: 在读取文档PDF的时候发生软件闪退的现象

### 问题描述 / What happened

在让AI处理文档内容时，在读取文档内容的过程中，发生闪退

### 环境 / Environment

- Cindy 版本或 commit / version or commit:0.1.69
- 平台与版本 / platform & OS version:Windows 11 x64
- 安装方式 / install method:通过Github安装包安装

### 复现步骤 / Steps to reproduce

1.让AI读取文档。
2.闪退.

### 日志与截图 / Logs & screenshots

[main-2026-09-02.log](https://github.com/user-attachments/files/31723360/main-2026-09-02.log)

Start by reproducing the crash while asking the AI to read a PDF on Windows 11 x64 with version 0.1.69, then inspect the linked main-2026-09-02.log for the failure point. Trace the PDF document-reading path from the reported error; done means PDF reading completes without the application closing unexpectedly.

Written by the indexing model from the issue text.