Never restore focus to hidden child.

Never restore focus to hidden child.

Don't set focus to a hidden window in our focus management code, this never
makes sense and results in apparent focus loss.

It also fixes, as a side effect, a crash in wxGrid under wxMSW as the focus is
not restored to the hidden grid editor any longer and so the code in its
wxEVT_KILL_FOCUS handler that resulted in the crash is not executed any
longer, see #13349.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@68319 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775