Fix closing minimized top level windows under Windows 10

Minimized windows don't seem to get any events after "Close" menu item
is selected from the system menu, so they were never actually destroyed
when closing them in this way.

Fix this by explicitly waking up the message loop after deleting the
window to ensure that the delayed destruction does happen.

Closes #18622.

See https://github.com/wxWidgets/wxWidgets/pull/1690

include/wx/msw/toplevel.h

@@ -55,6 +55,7 @@ public:
     virtual bool IsIconized() const wxOVERRIDE;
     virtual void SetIcons(const wxIconBundle& icons ) wxOVERRIDE;
     virtual void Restore() wxOVERRIDE;
+    virtual bool Destroy() wxOVERRIDE;
 
     virtual void SetLayoutDirection(wxLayoutDirection dir) wxOVERRIDE;