Prevent a leak detection crash when close() fails

[dkovba]

When an image is broken, container-core-images may crash with:

Application Specific Information:
_NIOFileSystem/SystemFileHandle.swift:131: Fatal error: Leaking file descriptor: the handle for '/Users/Dmitry/Library/Application Support/com.apple.container/content/ingest/03144D38-D98D-4833-9E0C-60229BF653D9/.tmp-MIB1oc' MUST be closed or detached with 'close()' or 'detachUnsafeFileDescriptor()' before the final reference to the handle is dropped.

Thread 9 Crashed:
0   libswiftCore.dylib            	       0x1adbfe110 _assertionFailure(_:_:file:line:flags:) + 176
1   container-core-images         	       0x105773628 closure #1 in SystemFileHandle.deinit + 424 (SystemFileHandle.swift:131)
2   container-core-images         	       0x10577365c partial apply for closure #1 in SystemFileHandle.deinit + 20
3   container-core-images         	       0x104ebd994 closure #1 in LockStorage.withLockedValue<A>(_:) + 124 (NIOLock.swift:183)
4   container-core-images         	       0x104ebde38 partial apply for closure #1 in LockStorage.withLockedValue<A>(_:) + 52
5   container-core-images         	       0x104c387fc ManagedBuffer<>.withUnsafeMutablePointers<A, B>(_:) + 152
6   container-core-images         	       0x104ebd8ec LockStorage.withLockedValue<A>(_:) + 172 (NIOLock.swift:180)
7   container-core-images         	       0x104ebe088 NIOLockedValueBox.withLockedValue<A>(_:) + 104 (NIOLockedValueBox.swift:38)
8   container-core-images         	       0x105773438 SystemFileHandle.deinit + 112 (SystemFileHandle.swift:128)
9   container-core-images         	       0x105773684 SystemFileHandle.__deallocating_deinit + 28
10  libswiftCore.dylib            	       0x1adaeef50 _swift_release_dealloc + 56
11  libswiftCore.dylib            	       0x1adaefabc bool swift::RefCounts<swift::RefCountBitsT<(swift::RefCountInlinedness)1>>::doDecrementSlow<(swift::PerformDeinit)1>(swift::RefCountBitsT<(swift::RefCountInlinedness)1>, unsigned int) + 152
12  container-core-images         	       0x104b81aac RegistryClient.fetchBlob(name:descriptor:into:progress:) + 180 (RegistryClient+Fetch.swift:200)
13  container-core-images         	       0x104b9f481 protocol witness for ContentClient.fetchBlob(name:descriptor:into:progress:) in conformance RegistryClient + 1
14  container-core-images         	       0x1049b6b29 ImageStore.ImportOperation.fetchBlob(_:) + 1 (ImageStore+Import.swift:167)
15  container-core-images         	       0x1049b5c6d ImageStore.ImportOperation.fetch(_:) + 1 (ImageStore+Import.swift:153)
16  container-core-images         	       0x1049b4f69 closure #1 in closure #1 in ImageStore.ImportOperation.fetchAll(_:) + 1 (ImageStore+Import.swift:126)
17  container-core-images         	       0x1049bb08d partial apply for closure #1 in closure #1 in ImageStore.ImportOperation.fetchAll(_:) + 1
18  libswift_Concurrency.dylib    	       0x2945e05f9 completeTaskWithClosure(swift::AsyncContext*, swift::SwiftError*) + 1

Replacing the SwiftNIO file handle with the Foundation file handle resolved the crash. However, this led to a worse performance:

Debug version:
SwiftNIO: 1:05s
Foundation: 1:18s (1.2 times worse)

Release version:
SwiftNIO: 0:34s
Foundation: 1:00s (1.8 times worse)

This PR attempts to prevent the crash without switching back to the Foundation file handle.