vcl: the docs say gdk_window_get_screen was added in GTK+ 2.24

Change-Id: Ib9b108c034181c0f94cbf86634447ba2d4afbaa5

vcl/unx/gtk/gdi/salnativewidgets-gtk.cxx

@@ -294,7 +294,7 @@ GdkX11Pixmap::GdkX11Pixmap( X11Pixmap& rOther, GdkWindow *pWindow )
 {
     GdkColormap* pColormap;
 
-#if GTK_CHECK_VERSION(2,10,0)
+#if GTK_CHECK_VERSION(2,24,0)
     GdkScreen *pScreen = gdk_window_get_screen( pWindow );
     mpGdkPixmap = gdk_pixmap_foreign_new_for_screen( pScreen, mpPixmap,
                                                      mnWidth, mnHeight,