Fix the issue that the downloaded chapters was not saved when download a comic without select chapters. Close #305

lib/network/download.dart

@@ -482,7 +482,7 @@ class ImagesDownloadTask extends DownloadTask with _TransferSpeedMixin {
       chapters: comic!.chapters,
       cover: File(_cover!.split("file://").last).name,
       comicType: ComicType(source.key.hashCode),
-      downloadedChapters: chapters ?? [],
+      downloadedChapters: chapters ?? comic?.chapters?.ids.toList() ?? [],
       createdAt: DateTime.now(),
     );
   }