蘋果iOS13 內購隱藏大坑：
- (void)productsRequest:(SKProductsRequest *)request didReceiveResponse:(SKProductsResponse *)response
iOS12之前是在主線程回調，
在iOS13改成了在一個異步線程回調，如果在iOS13下蘋果內購這個回調直接執行一些UI操作，則必然會提示
Modifications to the layout engine must not be performed from a background thread after it has been accessed from the main thread.