treat 0xc0c0c0 as transparent colour by default

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@24006 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

src/msw/gdiimage.cpp

@@ -356,6 +356,9 @@ bool wxBMPResourceHandler::LoadFile(wxBitmap *bitmap,
     bitmap->SetHeight(bm.bmHeight);
     bitmap->SetDepth(bm.bmBitsPixel);
 
+    // use 0xc0c0c0 as transparent colour by default
+    bitmap->SetMask(new wxMask(*bitmap, *wxLIGHT_GREY));
+
     return true;
 }