Fill transparency on the UI. Regression from commit
57450afb (DOCX import: declare wps as a
supported feature, 2013-12-03), as the VML import handled this.

Change-Id: I654b51d51448d25d400979a4a62189b86126ac01
Reviewed-on: https://gerrit.libreoffice.org/29517Reviewed-by: Miklos Vajna <vmiklos@collabora.co.uk>
Tested-by: Jenkins <ci@libreoffice.org>