related tdf#150557: fix unified transparence initialization with alpha

In 9831916428, shadow alpha
was passed in to UnifiedTransparencePrimitive2D instead of
shadow transparence mistakenly.

Fix that and pass shadow transparence instead.

Change-Id: Idabedade5d753961648683869cb077de0e4523eb
Reviewed-on: https://gerrit.libreoffice.org/c/core/+/156573
Tested-by: Jenkins
Reviewed-by: Sarper Akdemir <sarper.akdemir.extern@allotropia.de>

svx/source/sdr/primitive2d/sdrdecompositiontools.cxx

@@ -856,10 +856,8 @@ sal_uInt32 SlideBackgroundFillPrimitive2D::getPrimitive2DID() const
                 if (rShadow.getTransparence() != 0.0)
                 {
                     Primitive2DContainer aTempContent{ aRetval.back() };
-
-                    double fShadowAlpha = 1.0 - rShadow.getTransparence();
                     aRetval.back() = Primitive2DReference(new UnifiedTransparencePrimitive2D(
-                            std::move(aTempContent), fShadowAlpha));
+                            std::move(aTempContent), rShadow.getTransparence()));
                 }
             }