More fixes (again) (#858)

* Send stack trace to the UI on prod mode

* Pdfs will now generate cover images. I missed something a few releases ago.

API/Services/ReadingItemService.cs

@@ -86,6 +86,7 @@ public class ReadingItemService : IReadingItemService
             MangaFormat.Epub => _bookService.GetCoverImage(filePath, fileName),
             MangaFormat.Archive => _archiveService.GetCoverImage(filePath, fileName),
             MangaFormat.Image => _imageService.GetCoverImage(filePath, fileName),
+            MangaFormat.Pdf => _bookService.GetCoverImage(filePath, fileName),
             _ => string.Empty
         };
     }