Fix HasFocus() for composite controls.

Fix HasFocus() for composite controls.

Comparing the result of DoFindFocus() with the main window of composite
control doesn't work as it can return a child window so HasFocus() still
returned false for a composite control such as generic wxListCtrl even when it
did have focus.

Just use FindFocus() instead of DoFindFocus() to fix this.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@69788 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775