iOS 11 Crash purchase

### Platform
- [x] iOS
- [ ] macOS
- [ ] tvOS

### In-app purchase type
- [ ] Consumable
- [ ] Non-consumable
- [x] Auto-Renewable Subscription
- [ ] Non-Renewing Subscription

### Environment
- [ ] Sandbox
- [x] Production

### Version
ℹ SwiftyStoreKit (0.14.2)

## Report

### Issue summary
In the production version this bug started to appear when making a purchase

Crashed: com.apple.main-thread
```
0 libswiftFoundation.dylib 0x1067ad6b4 (Missing)
1 SwiftyStoreKit 0x10619d448 partial apply for thunk for @escaping @callee_guaranteed (@guaranteed RetrieveResults) -> () ()
2 SwiftyStoreKit 0x10619b38c closure #1 in ProductsInfoController.retrieveProductsInfo(_:completion:) ()
3 SwiftyStoreKit 0x10618c0c0 partial apply for closure #1 in InAppProductQueryRequest.performCallback(_:) (InAppProductQueryRequest.swift:76)
4 SwiftyStoreKit 0x106195240 thunk for @escaping @callee_guaranteed () -> () ()
5 libdispatch.dylib 0x182d3caa0 _dispatch_call_block_and_release + 24
6 libdispatch.dylib 0x182d3ca60 _dispatch_client_callout + 16
7 libdispatch.dylib 0x182d4965c _dispatch_main_queue_callback_4CF$VARIANT$mp + 1012
8 CoreFoundation 0x1833f3070 __CFRUNLOOP_IS_SERVICING_THE_MAIN_DISPATCH_QUEUE__ + 12
9 CoreFoundation 0x1833f0bc8 __CFRunLoopRun + 2272
10 CoreFoundation 0x183310da8 CFRunLoopRunSpecific + 552
11 GraphicsServices 0x1852f5020 GSEventRunModal + 100
12 UIKit 0x18d32d758 UIApplicationMain + 236
13 beelinguapp 0x10477cb88 main (Scheduler.swift:28)
14 libdyld.dylib 0x182da1fc0 start + 4
```