tdf#121111 ww8export: fillstyle_NONE needs a nil background

Without this, there is no way to cancel out an inherited
background color.

tdf#116071's unit test depends on this
fix in order to round-trip.

Change-Id: I99ad28ee87a6bea040e0ef3c712c1c911be70004
Reviewed-on: https://gerrit.libreoffice.org/64185
Tested-by: Justin Luth <justin_luth@sil.org>
Reviewed-by: Justin Luth <justin_luth@sil.org>
diff --git a/sw/source/filter/ww8/ww8atr.cxx b/sw/source/filter/ww8/ww8atr.cxx
index 5120aa5..44b3321 100644
--- a/sw/source/filter/ww8/ww8atr.cxx
+++ b/sw/source/filter/ww8/ww8atr.cxx
@@ -4216,8 +4216,26 @@
    }
}

void WW8AttributeOutput::FormatFillStyle( const XFillStyleItem& /*rFillStyle*/ )
void WW8AttributeOutput::FormatFillStyle( const XFillStyleItem& rFillStyle )
{
    // WW cannot have background in a section
    if ( !m_rWW8Export.m_bOutPageDescs )
    {
        // see MSWordExportBase::OutputItemSet for how _SOLID is handled
        if ( rFillStyle.GetValue() == drawing::FillStyle_NONE )
        {
            //Shd80Nil
            m_rWW8Export.InsUInt16( NS_sprm::sprmPShd80 );
            m_rWW8Export.InsUInt16( 0xffff );

            //cvAuto
            m_rWW8Export.InsUInt16( NS_sprm::sprmPShd );
            m_rWW8Export.pO->push_back( 10 );
            m_rWW8Export.InsUInt32( 0xFF000000 );
            m_rWW8Export.InsUInt32( 0xFF000000 );
            m_rWW8Export.InsUInt16( 0x0000 );
        }
    }
}

void WW8AttributeOutput::FormatFillGradient( const XFillGradientItem& /*rFillGradient*/ )