fix check for billing email when contributor isn't contact 1

[MegaphoneJon]

Overview

The check for billing address email still assumes contact 1 is always the contributor.

Steps to replicate:

• Create a webform with two contacts and a contribution.
• Contributor should be contact 2.
• Set "Number of Emails" for contact 1 to 0, and "Number of Emails" for contact 2 to 1 or more.
• Try to submit the payment.

Before

Error: An email address is required to complete this transaction.

After

No error.

Technical Details

Not all of the references to contact 1 were replaced by a reference to the contributor contact.