Fix widget data encoding crash — and possibly other bugs — by making sure that fetchArticlesAsync calls its callback just once. (The widget data encoder was crashing with multiple calls in the failure case, since it ended up having unbalanced DispatchGroup enter and leave calls.)

Account/Sources/Account/AccountManager.swift

@@ -370,25 +370,36 @@ public final class AccountManager: UnreadCountProvider {
 		var allFetchedArticles = Set<Article>()
 		let numberOfAccounts = activeAccounts.count
 		var accountsReporting = 0
+		var didCallCompletionBlock = false
+        var databaseFetchDidFail = false
+        
+        func callCompletion(_ result: ArticleSetResult) {
+            guard !didCallCompletionBlock else {
+                return
+            }
+            completion(result)
+            didCallCompletionBlock = true
+        }
         
 		guard numberOfAccounts > 0 else {
-			completion(.success(allFetchedArticles))
+			callCompletion(.success(allFetchedArticles))
 			return
 		}
 
 		for account in activeAccounts {
 			account.fetchArticlesAsync(fetchType) { (articleSetResult) in
+                precondition(Thread.isMainThread)
 				accountsReporting += 1
 
 				switch articleSetResult {
 				case .success(let articles):
 					allFetchedArticles.formUnion(articles)
-					if accountsReporting == numberOfAccounts {
-						completion(.success(allFetchedArticles))
+					if accountsReporting == numberOfAccounts && !databaseFetchDidFail {
+                        callCompletion(.success(allFetchedArticles))
 					}
 				case .failure(let databaseError):
-					completion(.failure(databaseError))
-					return
+                    databaseFetchDidFail = true
+                    callCompletion(.failure(databaseError))
 				}
 			}
 		}