gconfig: fix null pointer warning

In gconfig if you enable "Show all options", you'll see some "(null)"
config options, and clicking those options triggers a warning:

(gconf:9368): Gtk-CRITICAL **: gtk_text_buffer_insert_with_tags: assertion `text != NULL' failed
Signed-off-by: Li Zefan <lizf@cn.fujitsu.com>
Acked-by: Randy Dunlap <randy.dunlap@oracle.com>
Signed-off-by: Michal Marek <mmarek@suse.cz>

scripts/kconfig/gconf.c

@@ -1343,7 +1343,8 @@ static void update_tree(struct menu *src, GtkTreeIter * dst)
 #endif
 
 		if ((opt_mode == OPT_NORMAL && !menu_is_visible(child1)) ||
-		    (opt_mode == OPT_PROMPT && !menu_has_prompt(child1))) {
+		    (opt_mode == OPT_PROMPT && !menu_has_prompt(child1)) ||
+		    (opt_mode == OPT_ALL    && !menu_get_prompt(child1))) {
 
 			/* remove node */
 			if (gtktree_iter_find_node(dst, menu1) != NULL) {
@@ -1425,7 +1426,7 @@ static void display_tree(struct menu *menu)
 
 		if ((opt_mode == OPT_NORMAL && menu_is_visible(child)) ||
 		    (opt_mode == OPT_PROMPT && menu_has_prompt(child)) ||
-		    (opt_mode == OPT_ALL))
+		    (opt_mode == OPT_ALL    && menu_get_prompt(child)))
 			place_node(child, fill_row(child));
 #ifdef DEBUG
 		printf("%*c%s: ", indent, ' ', menu_get_prompt(child));