Don't reload broken thumbnails

Model/ThumbnailsModel.swift

@@ -0,0 +1,25 @@
+import Foundation
+
+final class ThumbnailsModel: ObservableObject {
+    @Published var unloadable = Set<URL>()
+
+    func insertUnloadable(_ url: URL) {
+        unloadable.insert(url)
+    }
+
+    func isUnloadable(_ url: URL!) -> Bool {
+        guard !url.isNil else {
+            return true
+        }
+
+        return unloadable.contains(url)
+    }
+
+    func loadableURL(_ url: URL!) -> URL? {
+        guard !url.isNil else {
+            return nil
+        }
+
+        return isUnloadable(url) ? nil : url
+    }
+}