Add a missing cast in g_object_set.

When NULL appears in variadic argument lists, it should be cast to the
pointer type that the function will be expecting, because otherwise it
might end up as a type not even the same size as a pointer.

unix/gtkdlg.c

@@ -2435,7 +2435,7 @@ GtkWidget *layout_ctrls(struct dlgparam *dp, struct Shortcuts *scs,
                             g_object_set(G_OBJECT(cellrend),
                                          "ellipsize", PANGO_ELLIPSIZE_END,
                                          "ellipsize-set", TRUE,
-                                         NULL);
+                                         (const char *)NULL);
                         }
 			column = gtk_tree_view_column_new_with_attributes
 			    ("heading", cellrend, "text", i+1, (char *)NULL);