Increment GlobalUser reference count on GuildUser creation

src/Discord.Net.WebSocket/Entities/Guilds/SocketGuild.cs

@@ -369,6 +369,7 @@ namespace Discord.WebSocket
             else
             {
                 member = SocketGuildUser.Create(this, Discord.State, model);
+                member.GlobalUser.AddRef();
                 _members[member.Id] = member;
                 DownloadedMemberCount++;
             }
@@ -381,6 +382,7 @@ namespace Discord.WebSocket
             else
             {
                 member = SocketGuildUser.Create(this, Discord.State, model);
+                member.GlobalUser.AddRef();
                 _members[member.Id] = member;
                 DownloadedMemberCount++;
             }
@@ -393,6 +395,7 @@ namespace Discord.WebSocket
             else
             {
                 member = SocketGuildUser.Create(this, Discord.State, model);
+                member.GlobalUser.AddRef();
                 _members[member.Id] = member;
                 DownloadedMemberCount++;
             }