Qt's interpretation of transparency is different from vcl's one

thanks Sergei Reznikov for pointing this out

Change-Id: Ib07d144bb50b178ee7b36f2c7b2eaede27ed10bc
(cherry picked from commit e56c81cc996747e3768cf171d0d6e94753b7d2af)

vcl/inc/qt5/Qt5Tools.hxx

@@ -58,7 +58,8 @@ inline Size toSize(const QSize& rSize) { return Size(rSize.width(), rSize.height
 
 inline QColor toQColor(const Color& rColor)
 {
-    return QColor(rColor.GetRed(), rColor.GetGreen(), rColor.GetBlue(), rColor.GetTransparency());
+    return QColor(rColor.GetRed(), rColor.GetGreen(), rColor.GetBlue(),
+                  255 - rColor.GetTransparency());
 }
 
 static constexpr QImage::Format Qt5_DefaultFormat32 = QImage::Format_ARGB32;