winemac: When programmatically focusing a window, don't generate WINDOW_LOST_FOCUS event for previously focused window.

That event can confuse things if the program switches focus from A to B and
then back to A and then processes events.  It will get an event saying that
A lost focus in Cocoa, check that A does indeed have current focus in Wine,
and so switch focus away from it (to the desktop window).  (It then gets an
event that B lost focus, but that does nothing at that point.)