get first unread chapter from original chapter list (#250)

The first unread chapter was retrieved from the filtered and sorted chapter list, which could result in e.g. incorrectly recognizing the latest released chapter as the first unread chapter.

Ideally the server would return the manga with its last read chapter, but this is currently not available.

src/components/manga/ChapterList.tsx

@@ -110,11 +110,11 @@ const ChapterList: React.FC<IProps> = ({ mangaId }) => {
 
     const firstUnreadChapter = useMemo(
         () =>
-            visibleChapters
+            chapters
                 .slice()
                 .reverse()
-                .find((c) => c.read === false),
-        [visibleChapters],
+                .find((chapter) => !chapter.read),
+        [chapters],
     );
 
     const handleSelection = (index: number) => {