Related tdf#156508 fix rendering of the About dialog .svg

After 0e7d4ea64f84bdc62c10692dcd97c3a32e72e16e, white polygons are
drawn in the LibreOffice about .svg in both the About dialog and with
the .svg in a document.

Creating the mask with COL_WHITE instead of COL_BLACK appears to fix
this without causing tdf#156508 to reoccur.

Change-Id: I886451245126c2b7f936e30275965148bf029627
Reviewed-on: https://gerrit.libreoffice.org/c/core/+/155362
Tested-by: Jenkins
Reviewed-by: Patrick Luby <plubius@neooffice.org>
diff --git a/drawinglayer/source/primitive2d/GlowSoftEgdeShadowTools.cxx b/drawinglayer/source/primitive2d/GlowSoftEgdeShadowTools.cxx
index 3c45fdd..f3909a1 100644
--- a/drawinglayer/source/primitive2d/GlowSoftEgdeShadowTools.cxx
+++ b/drawinglayer/source/primitive2d/GlowSoftEgdeShadowTools.cxx
@@ -35,7 +35,7 @@ AlphaMask ProcessAndBlurAlphaMask(const Bitmap& rMask, double fErodeDilateRadius
{
    // Only completely white pixels on the initial mask must be considered for transparency. Any
    // other color must be treated as black. This creates 1-bit B&W bitmap.
    BitmapEx mask(bConvertTo1Bit ? rMask.CreateMask(COL_WHITE) : rMask);
    BitmapEx mask(bConvertTo1Bit ? rMask.CreateMask(COL_BLACK) : rMask);

    // Scaling down increases performance without noticeable quality loss. Additionally,
    // current blur implementation can only handle blur radius between 2 and 254.