-在编辑状态下设置StoryCoverPage的Frame时(实际测试-》创建Story-》下拉-》Crash)因为未知原因导致在实机上测试出现'UICollectionView recieved layout attributes for a cell with an index path that does not exist: <NSIndexPath: 0xc000000000000016> {length = 2, path = 0 - 0}'的问题，所以此处添加判断以区分对待下拉时的显示效果