Don't send wxActivateEvent for minimized windows in wxMSW

Unexpectedly, minimizing the window by clicking on its taskbar icon resulted
in a wxActivateEvent. This broke the focus handling in wxTLW and resulted in
debug messages about ::SetFocus() failure whenever the window was minimized in
this way.

It also seems that other existing code doesn't take into account the
possibility of getting an "active" activation event when the window is
minimized and this doesn't happen in the other ports, so don't send this event
in wxMSW neither.

Closes #17128.

docs/changes.txt

@@ -167,6 +167,7 @@ wxMSW:
 - Avoid bogus assert after calling wxDatePickerCtrl::SetRange().
 - Add solution file for building with MSVS 2014 (Peter Tissen).
 - Correct wxGetOsDescription() for Windows 10 (Tobias Taschner).
+- Don't send wxActivateEvent for minimized windows (bzcdr).
 
 wxOSX/Cocoa: