Added support for missing or empty categories in cashshop_db.conf

- If a category in cashshop_db.conf is empty or missing, it will no
  longer show an error and/or insert an apple (dummy item).
- Corrected a mapserver startup crash in case cashshop_db is missing
  elements.
- Special thanks to Ind for providing official server/client info to
  handle the case of empty categories.

Signed-off-by: Haru <haru@dotalux.com>