fix: correctly sort books with a half-star rating.

When sorting by rating, books with a rating of a half-star aren't sorted
correctly. This was due to the ratings being converted to strings and
those strings used for sorting. A half-star is stored as 5, which means
that the string gets sorted as being above anything starting with 4 or
less. I.e. anything but a full five stars. This has been fixed by doing
the comparison on the int directly.

Author: rmarker

lib/ui/books_screen/books_screen.dart

@@ -396,8 +396,7 @@ class _BooksScreenState extends State<BooksScreen>
     }
 
     booksRated.sort((a, b) {
-      int ratingSorting = removeDiacritics(a.rating!.toString().toLowerCase())
-          .compareTo(removeDiacritics(b.rating!.toString().toLowerCase()));
+      int ratingSorting = a.rating!.compareTo(b.rating!);
       if (!isAsc) {
         ratingSorting *= -1;
       } // descending