CopyLastHeaderFooter doesn't do much good
if the previous section has blank stylenames.
(usually because of continuous section breaks).

Change-Id: Ida1e42ab0b650c7c43f06539b3cc058fe5c27919
Reviewed-on: https://gerrit.libreoffice.org/26911Tested-by: Jenkins <ci@libreoffice.org>
Reviewed-by: Justin Luth <justin_luth@sil.org>
Reviewed-by: Miklos Vajna <vmiklos@collabora.co.uk>