This is similar to commit 6bb241cc (ODT
export: fix lost <text:user-field-decl> for fields in tables in headers,
2019-05-29), but here the container we want to ignore (between the
header and the field) is a text frame, not a table cell.

Change-Id: I6e8006fbd666802070cfeb88ca4528c66cc6d559
Reviewed-on: https://gerrit.libreoffice.org/73205Reviewed-by: Miklos Vajna <vmiklos@collabora.com>
Tested-by: Jenkins