Fix compilation of new wxNotificationMessage for wxGTK without libnotify.

Add the wxUSE_LIBNOTIFY check forgotten by the previous commit.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@72219 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

src/gtk/notifmsg.cpp

@@ -23,7 +23,7 @@
     #pragma hdrstop
 #endif
 
-#if wxUSE_NOTIFICATION_MESSAGE
+#if wxUSE_NOTIFICATION_MESSAGE && wxUSE_LIBNOTIFY
 
 #ifndef WX_PRECOMP
 #endif // WX_PRECOMP
@@ -191,4 +191,4 @@ wxNotificationMessage::~wxNotificationMessage()
         g_object_unref(m_notification);
 }
 
-#endif // wxUSE_NOTIFICATION_MESSAGE
+#endif // wxUSE_NOTIFICATION_MESSAGE && wxUSE_LIBNOTIFY