BUG FIX on address.php

When you have customs fields associated with shipping address, that are requiered and have been left in blank by the user, a bug exist in which the custom field is not marked in red, and the explain text is not displayed.

This code Fix the bug

pd: I have spent 6 hours to figure it out because i'm new to opencart.

Regards
Merge pull request #1973 from CoverUp/patch-1

BUG FIX on address.php