wxOSX's wxApp::MacReopenApp() previously contained logic to unhide
hidden windows, but this code was commended out since 2013 as
problematic - it was showing windows like closed, but not yet
destroyed, non-modal dialogs.
Unfortunately while this part was commented out, the rest of the code
that handled existence of hidden windows was not, resulting in a bug
where nothing happened after clicking app icon in the Dock if the
application didn't have any visible window at the moment, but had a
"technical" hidden one, e.g. after opening and closing
wxPreferencesEditor.
Fixed by simplyfing and removing all (functionally commented-out) code
related to hidden windows. Instead, the logic is now:
1. do nothing if some window is already visible
2. restore an iconized window if there's one
3. call MacNewFile() if neither happened
c8f4d5e669