fix: Restrictions on /invite

- Don't allow a player to be invited if they exist in a different game
  mode.
- Restrict party size to 4 if gamemode is bitterblack maze.

Arrowgene.Ddon.GameServer/Chat/Command/Commands/PartyInviteCommand.cs

@@ -2,6 +2,7 @@
 using Arrowgene.Ddon.GameServer.Characters;
 using Arrowgene.Ddon.GameServer.Handler;
 using Arrowgene.Ddon.Shared.Entity.PacketStructure;
+using Arrowgene.Ddon.Shared.Model;
 using Arrowgene.Ddon.Shared.Network;
 using System.Collections.Generic;
 using System.Linq;
@@ -43,6 +44,12 @@ public override void Execute(string[] command, GameClient client, ChatMessage me
                 return;
             }
 
+            if (client.GameMode == GameMode.BitterblackMaze && client.Party.Members.Count >= 4)
+            {
+                responses.Add(ChatResponse.CommandError(client, "This game mode only supports 4 players."));
+                return;
+            }
+
             if (!client.Party.GetPlayerPartyMember(client).IsLeader)
             {
                 responses.Add(ChatResponse.CommandError(client, "Only the party leader can invite."));
@@ -112,6 +119,12 @@ public override void Execute(string[] command, GameClient client, ChatMessage me
                     return;
                 }
 
+                if (targetClient.GameMode != client.GameMode)
+                {
+                    responses.Add(ChatResponse.CommandError(client, "You cannot invite players which are in different game modes."));
+                    return;
+                }
+
                 if (client.Party.Contains(targetClient.Character))
                 {
                     responses.Add(ChatResponse.CommandError(client, "The party already contains that player."));