Set the window in focus event sent by wxComboCtrl correctly.

Set the window in focus event sent by wxComboCtrl correctly.

The window parameter wasn't copied correctly in the forwarded event. Fix this
and avoid future problems of the same kind by using the copy ctor for creating
the new event and then override the fields that we need to change from the
original event instead of recreating the new event from bits and pieces of the
original one.

Closes #12741.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@66314 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775