/// <summary>
 /// Fetches the thumbnail for the given asset.
 /// </summary>
 /// <param name="asset">The asset for which to fetch the thumbnail.</param>
 /// <param name="options">The extra options, if any (can be null).</param>
 /// <param name="callback">The callback to call when the fetch finishes (optional).</param>
 public static void FetchThumbnail(PolyAsset asset, PolyFetchThumbnailOptions options,
                                   FetchThumbnailCallback callback = null)
 {
     CheckInitialized();
     PolyMainInternal.Instance.FetchThumbnail(asset, options, callback);
 }