Fixed FedEx API Error

FedEx API docs state that `StateOrProvinceCode` is *"Required if Sender Country Code is US or CA."*, but OpenCart was sending the full state/province name when not US, causing FedEx to respond with the error *"The length of the destination state or province exceeds the limit of 2 characters."* This issue is fixed by sending an empty `StateOrProvinceCode` when not in US/CA.