Fix issues with missing order total modules

Several problems can occur if you update your osCommerce database from a fresh version of the source without your old order total modules.  You will only see the order total module in the "Install Module" section.  But the trouble is, from there, if you try to edit, it won't work, and if you try to remove it will remove the wrong thing.  And you can wind up trying to add the module several times, which will put duplicate keys in your database.  This PR adds a fix for the remove problem so the right thing is removed, a workaround for the edit problem so the wrong thing isn't edited, and a fix for the duplicate key issue, by checking > 0 rather than == 1.