Disable warning

Source/DataLayer/EfClasses/Book.cs

@@ -45,7 +45,9 @@ namespace DataLayer
 
 		//This field is now unused, however, there is little sense in adding a
 		//database migration to remove an unused field. Leave it for compatibility.
+#pragma warning disable CS0649 // Field 'Book._audioFormat' is never assigned to, and will always have its default value 0
 		internal long _audioFormat;
+#pragma warning restore CS0649
 
         // mutable
         public string PictureId { get; set; }