Fix crash inserting present items when currentItems includes posts from since-unfollowed users

Tusker/Screens/Timeline/TimelineViewController.swift

@@ -467,9 +467,19 @@ class TimelineViewController: UIViewController, TimelineLikeCollectionViewContro
             return
         }
         let currentItems = snapshot.itemIdentifiers(inSection: .statuses)
-        if case .status(id: let firstID, _, _) = currentItems.first,
+        func currentItemsContains(id: String) -> Bool {
+            return currentItems.contains { item in
+                switch item {
+                case .status(id: id, collapseState: _, filterState: _):
+                    return true
+                default:
+                    return false
+                }
+            }
+        }
         // if there's no overlap between presentItems and the existing items in the data source, prompt the user
-           !presentItems.contains(firstID) {
+        // we can't be clever here by just checking the first id in currentItems against presentItems, since that may belong to a since-unfollowed user
+        if !presentItems.contains(where: { currentItemsContains(id: $0) }) {
             let applySnapshotBeforeScrolling: Bool
             
             // remove any existing gap, if there is one