The background tab page uses SvxBrushItem. Area tab page uses
XFillBitmapItem. setSvxBrushItemAsFillAttributesToTargetSet creates
empty string for XFillBitmapItem name. Bitmap can be identified by
GraphicObject::GetUniqueId. Use this to select bitmap in bitmap tab page
bitmap list.

Change-Id: Ic739c0b462502a986358bf00acfbac01fafd19f7
Reviewed-on: https://gerrit.libreoffice.org/66838
Tested-by: Jenkins
Reviewed-by: Jim Raykowski <raykowj@gmail.com>
(cherry picked from commit 6850fcef)
Reviewed-on: https://gerrit.libreoffice.org/71855Reviewed-by: Katarina Behrens <Katarina.Behrens@cib.de>