Update DM channel on entity updates.

src/Discord.Net.WebSocket/Entities/Users/SocketGlobalUser.cs

@@ -1,4 +1,5 @@
 using System.Diagnostics;
+using System.Linq;
 using Model = Discord.API.User;
 using PresenceModel = Discord.API.Presence;
 
@@ -51,6 +52,7 @@ namespace Discord.WebSocket
         internal void Update(ClientState state, PresenceModel model)
         {
             Presence = SocketPresence.Create(model);
+            DMChannel = state.DMChannels.FirstOrDefault(x => x.Recipient.Id == Id);
         }
         
         internal new SocketGlobalUser Clone() => MemberwiseClone() as SocketGlobalUser;