message: Document special case in `ExpectMapClientRequestData`
diff: @@ -112,7 +112,7 @@ struct ExpectMapClientRequestData
  uint64_t m_client_id;
  uint8_t m_access_level;
  ACE_INET_Addr m_from_addr;
  - QString char_from_db_data; //! serialized character data.
  + QString char_from_db_data; //! serialized character data, if this is empty Map server assumes a new character
  uint16_t m_slot_idx;
  QString m_character_name;
  QString m_map_name;
  