Fix AudioDb album description not displayed when only base strDescription field is populated

TheAudioDB returns the English album description in the base strDescription
field (no language suffix). The plugin previously only read strDescriptionEN,
which is absent from the API response, so the Overview/Description field
stayed empty for English (and any other language for which no localized
strDescription<LANG> exists). Mirror the fallback already applied to
AudioDbArtistProvider in #16606 and add the missing strDescription property
to the Album DTO.

Fixes #17080

MediaBrowser.Providers/Plugins/AudioDb/AudioDbAlbumProvider.cs

@@ -142,7 +142,9 @@ namespace MediaBrowser.Providers.Plugins.AudioDb
 
             if (string.IsNullOrWhiteSpace(overview))
             {
-                overview = result.strDescriptionEN;
+                overview = string.IsNullOrWhiteSpace(result.strDescriptionEN)
+                    ? result.strDescription
+                    : result.strDescriptionEN;
             }
 
             item.Overview = (overview ?? string.Empty).StripHtml();
@@ -240,6 +242,8 @@ namespace MediaBrowser.Providers.Plugins.AudioDb
 
             public string strAlbumCDart { get; set; }
 
+            public string strDescription { get; set; }
+
             public string strDescriptionEN { get; set; }
 
             public string strDescriptionDE { get; set; }