h > ms_buffer->GetHeight() )
{
delete ms_buffer;
+
+ // we must always return a valid bitmap but creating a bitmap of
+ // size 0 would fail, so create a 1*1 bitmap in this case
+ if ( !w )
+ w = 1;
+ if ( !h )
+ h = 1;
+
ms_buffer = new wxBitmap(w, h);
}