[Bug]：载入大尺寸图片启动宫格功能，连续点击两次左上角完成宫格程序自动退出

[liyongchao911]

Thanks for your bug report. To help us solve the issue better, please provide following information：

1. PaddleSeg version: (please specify the branch as well，e.g. PaddleSeg release/2.3)
2. PaddlePaddle version: (e.g. PaddlePaddle 2.1.0)
3. Operation system: (e.g. Linux/Windows/MacOS)
4. Python version: (e.g. Python3.6/7/8)
5. CUDA/cuDNN version: (e.g. CUDA10.2/cuDNN 7.6.5)
6. Full codes: (if you modify any original code，please show the comparison of the codes before and after)
7. Detailed error information, releated running log: (if using multi-gpus，the log is saved to log/worklog.0 by default)
8. Running command or reproduce details：
9. Additional context: (Add any other context about the problem)

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欢迎您反馈PaddleSeg使用问题，辛苦您提供以下信息，方便我们快速定位和解决问题：

1. PaddleSeg版本： release/2.5
2. PaddlePaddle版本：PaddlePaddle 2.2.0
3. 操作系统信息：Windows10
4. Python版本号：3.7
5. CUDA/cuDNN版本：
6. 详细的错误信息、相关log：载入大尺寸图片启动宫格功能，连续点击两次左上角完成宫格程序自动退出， 命令行终端爆出的错误为： AttributeError: 'NoneType' object has no attribute 'splicingList'