Somewhat magically, just adding XATTR to the FlySet makes
background colors/gradients/images appear. This has been
broken since XATTR was introduced in LO 4.3.

Change-Id: I84554045f49618a5eb927edfebdf641c5a93b673
Reviewed-on: https://gerrit.libreoffice.org/66310
Tested-by: Jenkins
Reviewed-by: Justin Luth <justin_luth@sil.org>