Comment improvements broke docx export.

[gokaysatir]

For providing parent - child relationship for comments, we made some improvements to the code. But the one for keeping the parent - child relations of comments when copying breaks the docx export somehow.

Regressing commit can be found here:

• https://gerrit.libreoffice.org/c/core/+/177396

Steps to reproduce:

• Open attached file with co25.04 or a version containing above commit.
• Save it.
• Open it with Word.
• An error raises.

SampleFile.docx