当用户点击两次购买Iap确认按钮时，使用以下方法分析CRASHES：
Fatal Exception: NSInternalInconsistencyException
"You cannot purchase a product that is in the process of being purchased"
PFPurchase.m line 108
真的要由应用程序来阻止这种情况吗？
[解析1.4.1]