Set proper value of wxSpinEvent generated by wxSpinCtrl

Current way of converting wxSpinCtrl value to integer does not work
for negative values. We can just use here integer value returned
by GetValue().

Closes #18802.

src/generic/spinctlg.cpp

@@ -652,7 +652,7 @@ void wxSpinCtrl::DoSendEvent()
 {
     wxSpinEvent event( wxEVT_SPINCTRL, GetId());
     event.SetEventObject( this );
-    event.SetPosition((int)(m_value + 0.5)); // FIXME should be SetValue
+    event.SetPosition(GetValue());
     event.SetString(m_textCtrl->GetValue());
     GetEventHandler()->ProcessEvent( event );
 }