include hidden items in /modifyinv autocomplete#773

right now no hidden items will appear in the autocomplete for any /modifyinv slash command, but they still work if you type out the full item name and send the command which is a bit annoying since the items autocomplete properly in all other /shop editing commands (and iirc using either of those commands require the same permissions). it doesnt feel too different from having to use autoresponders to edit inventories :’)