str_pad breaks lookups for postcodes under 1000

With postcodes under 1000, lookups don't work. This is because the database stores the postcode 800 as '0800', and the lookup at time of calculating shipping options selects where dest_zip='800'.

I've removed the str_pad so solve this issue. The other option would be to pad during lookup. I'm not sure what the value is in padding it out as input time though.