Fixed multi-threading crash when copying a store

[sgruby]

When the store is a .directory type and public func copy(to targetURL: URL) throws is called, the copy in that method is performed on the backgroundContext. In the private func copy(to targetURL: URL, tempURL: URL, blobs: BlobStore) that is called, the manifest is created using LoggerStoreInfo which calls try messageCount() and try networkRequestsCount(). Both of these methods do their fetch using container.viewContext which is a different thread leading to a crash.

You can verify the crash by using the com.apple.CoreData.ConcurrencyDebug 1 runtime flag (see [https://oleb.net/blog/2014/06/core-data-concurrency-debugging/](Core Data Concurrency Debugging) and then exporting the LoggerStore.

By getting the counts on the same thread, this crash is eliminated.

[kean]

Thanks for the fix. I'm merging and pushing a patch now.