Saving gets stuck in Realtime editor if a page mandatory title is not provided before saving

Steps to reproduce

1. Login as Admin
2. Go to "Administer Wiki" > "Editing" > "Edit Mode"
3. Change "Make page title field mandatory" to 'Yes'
4. Click "Save"
5. Click "Create" button to create a page (or use an existing page)
6. Fill in a page name
7. (Optional): Type some page content
8. Delete everything in the page "Title" field
9. Click "Done" button

Expected results

If the "Title" field is not filled, clicking the "Done" button has no effect (the button is either deactivated or doesn't perform any action) until a page Title is provided.

Actual results

The "Done" button become deactivated and the status in the right side of the bar says "Saving", but the circle spins endlessly.

The same happens now when clicking "Summarize & Done", the "Done" button from the modal is not active.

Even if a page title is provided at this point, there is nothing the user can do, except navigating away or refresh the page, but the page content gets lost either way.

No errors in JS console.

The issue doesn't reproduce if the page is edited without Realtime editor.

Tested and reproduced on XWiki 16.10.8 as well.