xmloff: make the export of the horrible field marks aware of auto-styles

When exporting the .DOC bugdoc of fdo#87110 to ODF, the auto-styles
export will iterate over the fieldmarks in the page header and add the
attributes for them but not export the elements, so the first auto-style
gets a bunch of duplicate attributes.

Change-Id: I3fcf39f03e3d9ae5fca661efa7eb4bbb3eab9f5c
(cherry picked from commit 06f85d41d02ebef76487b230f35f2ec638c46c8b)
Reviewed-on: https://gerrit.libreoffice.org/13426
Reviewed-by: Miklos Vajna <vmiklos@collabora.co.uk>
Tested-by: Miklos Vajna <vmiklos@collabora.co.uk>