Change wxNotebook selection before sending page changed event in wxMSW.

Change wxNotebook selection before sending page changed event in wxMSW.

wxEVT_COMMAND_NOTEBOOK_PAGE_CHANGED handler should see the new page selected
in the control, not the old one as was the case if the page was changed using
the mouse in wxMSW.

This should have been done together with the other changes of r66224, see its
commit message for more details.

Closes 13145.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@67589 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775