FIX] Update TypingStartedEvent model (#2702)

Author: Misha-133

src/Discord.Net.WebSocket/API/Gateway/TypingStartEvent.cs

@@ -9,9 +9,9 @@ internal class TypingStartEvent
         [JsonProperty("channel_id")]
         public ulong ChannelId { get; set; }
         [JsonProperty("guild_id")]
-        public ulong GuildId { get; set; }
+        public Optional<ulong> GuildId { get; set; }
         [JsonProperty("member")]
-        public GuildMember Member { get; set; }
+        public Optional<GuildMember> Member { get; set; }
         [JsonProperty("timestamp")]
         public int Timestamp { get; set; }
     }

src/Discord.Net.WebSocket/DiscordSocketClient.cs

@@ -2046,8 +2046,8 @@ private async Task ProcessMessageAsync(GatewayOpCode opCode, int? seq, string ty
                                     var user = (channel as SocketChannel)?.GetUser(data.UserId);
                                     if (user == null)
                                     {
-                                        if (guild != null)
-                                            user = guild.AddOrUpdateUser(data.Member);
+                                        if (guild != null && data.Member.IsSpecified)
+                                            user = guild.AddOrUpdateUser(data.Member.Value);
                                     }
                                     var cacheableUser = new Cacheable<IUser, ulong>(user, data.UserId, user != null, async () => await GetUserAsync(data.UserId).ConfigureAwait(false));