Add placeholders

Model/Applications/PipedAPI.swift

@@ -232,6 +232,8 @@ final class PipedAPI: Service, ObservableObject, VideosAPI {
             if let channel = extractChannel(from: content) {
                 return ContentItem(channel: channel)
             }
+        default:
+            return nil
         }
 
         return nil

Model/Applications/VideosAPI.swift

@@ -74,6 +74,8 @@ extension VideosAPI {
         case .playlist:
             urlComponents.path = "/playlist"
             queryItems.append(.init(name: "list", value: item.playlist.id))
+        default:
+            return nil
         }
 
         if !time.isNil, time!.seconds.isFinite {