Ensure that 32bpp bitmaps selected in wxMemoryDC use DIB for their internal representation as GDI+ functions don't seem to work correctly with DDBs with alpha channel. Closes #13328. git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/branches/WX_3_0_BRANCH@75765 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775