use gptp api + logic fix

Instead of using 004889D0 = GetFreeSupply(unit_id, playerid) from scbw, because unit id's are subject to change during the development of hydra, using gptp's api call to request the same number using player id and race. This should be more future proof (thanks Veeq).

Also fixing logical mistake, which in some AI scripts caused supply to discontinue production when supply was equal to current max.