Add default ctor and Init() method to wxMSW private AutoHBITMAP class. This doesn't change anything for now but will be used by an upcoming commit. git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@65958 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775