clist: corrupt removed entry pointers if DEBUG

kernel/clist.c

@@ -1,6 +1,7 @@
 /* See the end of this file for copyright and license terms. */
 
 #include <gay/clist.h>
+#include <gay/config.h>
 
 void clist_init(struct clist *head)
 {
@@ -30,6 +31,11 @@ void clist_del(struct clist *node)
 {
 	node->next->prev = node->prev;
 	node->prev->next = node->next;
+
+#	ifdef DEBUG
+		node->next = NULL;
+		node->prev = NULL;
+#	endif
 }
 
 /*