fix typo in chan sip that causes segV

git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@3931 65c4cc65-6c06-0410-ace0-fbb531ad65f3

channels/chan_sip.c

@@ -8786,7 +8786,7 @@ static void delete_users(void)
 	for (user=userl.users;user;) {
 		userlast = user;
 		user=user->next;
-		destroy_user(user);
+		destroy_user(userlast);
 	}
 	userl.users=NULL;
 	ast_mutex_unlock(&userl.lock);