Playerbots: Fix build error caused by iterator refactor

Recently, `GetPlayerBotsBegin()` and `GetPlayerBotsEnd()` were removed from the PlayerBots code in favor of a new function called `ForEachPlayerbot()`. `ChatHandler.cpp` seems to have been the only file that was using the old functions, everything builds fine with this fix.

src/game/Chat/ChatHandler.cpp

@@ -390,14 +390,13 @@ void WorldSession::HandleMessagechatOpcode(WorldPacket& recv_data)
             PlayerbotMgr* mgr = GetPlayer()->GetPlayerbotMgr();
             if (mgr && GetPlayer()->GetGuildId())
             {
-                for (PlayerBotMap::const_iterator it = mgr->GetPlayerBotsBegin(); it != mgr->GetPlayerBotsEnd(); ++it)
+                mgr->ForEachPlayerbot([&](Player* const bot)
                 {
-                    Player* const bot = it->second;
                     if (bot->GetGuildId() == GetPlayer()->GetGuildId())
                     {
                         bot->GetPlayerbotAI()->HandleCommand(type, msg, *GetPlayer(), lang);
                     }
-                }
+                });
             }
 
             sRandomPlayerbotMgr.HandleCommand(type, msg, *_player, "", GetPlayer()->GetTeam(), lang);