修复 AWList_iterator 的一个BUG

AWList.c

@@ -103,12 +103,20 @@ AWNode* AWList_find_node(AWList* list,
   return NULL;
 }
 
-AWNode* AWList_iterator(AWList* list) {
-  if (!list || list->iter == list->tail->next) return NULL;
+AWNode *AWList_iterator(AWList *list)
+{
+	if (!list || list->iter == list->tail->next)
+		return NULL;
 
-  if (list->iter == list->head) list->iter = list->head->next;
+	if (list->iter == list->head) {
+		list->iter = list->head->next;
+	}
 
-  AWNode* iter = list->iter;
-  list->iter   = list->iter->next;
-  return iter;
+	AWNode *iter = list->iter;
+
+	if (list->iter) {
+		list->iter = list->iter->next;
+	}
+
+	return iter;
 }