Changes in the document are lost upon save if the content serialization fails

This issue was reproduced on version 9.11.3 of XWiki with both CKEditors 1.20 and 1.25, on Chrome.

Steps to reproduce:

• "break" a document in the editor, as described in issue CKEDITOR-227
• after having done the cut and paste, add some additional content in the document, for example a new paragraph or something.
• hit save or save and continue
  • See the exception on wysiwyg serialization in the attachments of issue CKEDITOR-227

Actual result

• The save proceeds with no error, but no changes are saved in the document: neither the cut and paste, nor the content added in the same editing session
• No warning is displayed to the user

Expected result

• If the CKEditor cannot recover from the exception, the user should stay in edit mode with the editor showing the content that they added and the user should be warned that their content could not be saved, allowing to copy-paste the content somewhere to not lose it.