Follow-up to Global_Functino updates (834f3ba).
"F_GetPlural" now works for most item/mob cases, but still does not detect inputs that are already pluralized.
- For formats "... of|in|on ..." (ex. Piece of Cake), preceding word will be pluralized (ex. Pieces).
- Added some additional checks to prevent common errors.

Signed-off-by: Euphy <euphy.raliel@rathena.org>