Fix the integer value in events generated by generic wxSpinCtrl

This notably fixes the problem with changing the year using spin control
arrows under macOS, where this control is used as part of
wxGenericCalendarCtrl, as not having the correct value in the event object
resulted in bogus events with dates in the year 0 there.

Closes http://trac.wxwidgets.org/ticket/17193

src/generic/spinctlg.cpp

@@ -96,6 +96,7 @@ public:
         wxCommandEvent eventCopy(event);
         eventCopy.SetEventObject(m_spin);
         eventCopy.SetId(m_spin->GetId());
+        eventCopy.SetInt(wxAtoi(event.GetString()));
         m_spin->ProcessWindowEvent(eventCopy);
     }