pdftocio throws error when saving

Hi, I'm trying to use `pdftocio` to generate a ToC for a pdf. I have already generated the toc file using `pdfxmeta` and 'pdftocgen`. The error is as following:
```
Traceback (most recent call last):
File "/home/amzon-ex/.local/bin/pdftocio", line 8, in
sys.exit(main())
^^^^^^
File "/home/amzon-ex/.local/lib/python3.11/site-packages/pdftocio/app.py", line 163, in main
doc.save(out)
File "/home/amzon-ex/.local/lib/python3.11/site-packages/fitz/fitz.py", line 4710, in save
return _fitz.Document_save(self, filename, garbage, clean, deflate, deflate_images, deflate_fonts, incremental, ascii, expand, linear, no_new_id, appearance, pretty, encryption, permissions, owner_pw, user_pw)
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
RuntimeError: cannot find object in xref (2818 0 R)
```

Can you help?

Start in pdftocio/app.py at the main function and the doc.save(out) call shown in the traceback. Reproduce the failure with the same pdftocio, pdfxmeta, and pdftocgen workflow, then determine which input PDF or save condition causes the missing xref object. Done means the reported PDF saves successfully or the failure is handled with a clear explanation.

Written by the indexing model from the issue text.