Fix crash when conversation VC tries to restore from unloaded status

Tusker/Screens/Conversation/ConversationTableViewController.swift

@@ -131,7 +131,31 @@ class ConversationTableViewController: EnhancedTableViewController {
         let initialImage = showStatusesAutomatically ? ConversationTableViewController.hidePostsImage : ConversationTableViewController.showPostsImage
         visibilityBarButtonItem = UIBarButtonItem(image: initialImage, style: .plain, target: self, action: #selector(toggleVisibilityButtonPressed))
         navigationItem.rightBarButtonItem = visibilityBarButtonItem
-
+        
+        loadMainStatus()
+    }
+    
+    private func loadMainStatus() {
+        if let mainStatus = mastodonController.persistentContainer.status(for: mainStatusID) {
+            self.mainStatusLoaded(mainStatus)
+        } else {
+            let request = Client.getStatus(id: mainStatusID)
+            mastodonController.run(request) { (response) in
+                switch response {
+                case let .success(status, _):
+                    let viewContext = self.mastodonController.persistentContainer.viewContext
+                    self.mastodonController.persistentContainer.addOrUpdate(status: status, incrementReferenceCount: false, context: viewContext) { (statusMO) in
+                        self.mainStatusLoaded(statusMO)
+                    }
+                    
+                case .failure(_):
+                    fatalError()
+                }
+            }
+        }
+    }
+    
+    private func mainStatusLoaded(_ mainStatus: StatusMO) {
         let mainStatusItem = Item.status(id: mainStatusID, state: mainStatusState)
         
         var snapshot = NSDiffableDataSourceSnapshot<Section, Item>()
@@ -139,12 +163,10 @@ class ConversationTableViewController: EnhancedTableViewController {
         snapshot.appendItems([mainStatusItem], toSection: .statuses)
         dataSource.apply(snapshot, animatingDifferences: false)
 
-        guard let mainStatus = self.mastodonController.persistentContainer.status(for: self.mainStatusID) else {
-            fatalError("Missing cached status \(self.mainStatusID)")
-        }
         let mainStatusInReplyToID = mainStatus.inReplyToID
         mainStatus.incrementReferenceCount()
 
+        // todo: it would be nice to cache these contexts
         let request = Status.getContext(mainStatusID)
         mastodonController.run(request) { response in
             guard case let .success(context, _) = response else { fatalError() }