Minor linked lists bug fix. When you're dealing with swapping entries around a lot it can cause a seg fault.

git-svn-id: https://origsvn.digium.com/svn/asterisk/branches/1.2@19303 65c4cc65-6c06-0410-ace0-fbb531ad65f3

include/asterisk/linkedlists.h

@@ -439,6 +439,7 @@ struct {								\
 		if ((head)->last == (elm))				\
 			(head)->last = curelm;				\
 	}								\
+        (elm)->field.next = NULL;                                       \
 } while (0)
 
 #endif /* _ASTERISK_LINKEDLISTS_H */