Default product EUC not working

In `commerce_exactor_euc.module` on line 90, the field configuration attempts to set the default value for the product "Exactor EUC" field to 'EUC-09020802', which is for general taxable retail items. It does so by using `isset()` to check if there is already a value for this field on the product.

On my site, the value on the product is already set to empty string, so isset() returns true, so the field's default value becomes empty string. This causes the default to effectively become the first item in the select list, which happens to be software. This causes tax not to be assessed in certain cases if someone doesn't manually set the field to the intended default value.

Changing `isset()` to `!empty()` makes it default as intended.

I'd like to submit a patch making this change.