fix: distinct image language list before use

in case the transformed main language was already in the list

Shoko.Server/Providers/TMDB/TmdbMetadataService.cs

@@ -1456,6 +1456,7 @@ private async Task DownloadEpisodeImages(int episodeId, int showId, int seasonNu
     private List<TitleLanguage> GetLanguages(TitleLanguage? mainLanguage = null) => _settingsProvider.GetSettings().TMDB.ImageLanguageOrder
         .Select(a => a is TitleLanguage.Main ? mainLanguage is not TitleLanguage.None and not TitleLanguage.Unknown ? mainLanguage : null : a)
         .WhereNotNull()
+        .Distinct()
         .ToList();
 
     #endregion