Use 0 instead of NULL to avoid g++ warning.

g++ (usefully) warns when assigning NULL to a non-pointer in wxGDIPlusRenderer.

Just use 0 instead of NULL to avoid the warning.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@68586 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

src/msw/graphics.cpp

@@ -1906,7 +1906,7 @@ void wxGDIPlusRenderer::Unload()
     if ( m_gditoken )
     {
         GdiplusShutdown(m_gditoken);
-        m_gditoken = NULL;
+        m_gditoken = 0;
     }
     m_loaded = -1; // next Load() will try again
 }