fix:选中分类，分类下PPT默认按照PPT创建时间降序排列，若手动移动了排序，则以用户手动移动的为准。

models/ppt_v2_group_mapping.go

@@ -38,7 +38,7 @@ func GetPptMappingCountByGroupId(groupId int64) (total int64, err error) {
 // GetPptMappingListByGroupId 查询目录下，ppt列表
 func GetPptMappingListByGroupId(groupId int64) (list []*PptV2GroupMapping, err error) {
 	o := orm.NewOrmUsingDB("rddp")
-	sql := `select group_ppt_id, group_id, ppt_id, ppt_sort, admin_id, admin_real_name, create_time from ppt_v2_group_mapping where group_id=? order by ppt_sort asc, group_ppt_id asc `
+	sql := `select group_ppt_id, group_id, ppt_id, ppt_sort, admin_id, admin_real_name, create_time from ppt_v2_group_mapping where group_id=? order by ppt_sort asc, group_ppt_id desc `
 	_, err = o.Raw(sql, groupId).QueryRows(&list)
 	return
 }