fix sharded client current user (#1947)

src/Discord.Net.WebSocket/DiscordShardedClient.cs

@@ -498,6 +498,9 @@ namespace Discord.WebSocket
         #endregion
 
         #region IDiscordClient
+        /// <inheritdoc />
+        ISelfUser IDiscordClient.CurrentUser => CurrentUser;
+
         /// <inheritdoc />
         async Task<IApplication> IDiscordClient.GetApplicationInfoAsync(RequestOptions options)
             => await GetApplicationInfoAsync().ConfigureAwait(false);