Display and sort names should be populated with email address when contribution form only has email address

• • • This is a regression from 4.4
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      When anonymous users complete online contribution form which only collects an email address, the sort and display names should both be populated with the submitted email address. This works properly in 4.4. In 4.5, both columns are left NULL.

To recreate:

• Enable pay later for sample contribution page id=1
• Log out and complete the contribution form selecting Pay Later option (you will pick an amount and enter an Email Address)
• Log back in and check the new record. The Contact Summary looks quite weird because there's no title / display name (see attached screenshot). Both sort and display names are NULL in the DB record.

NOTE: Same steps populate sort and display properly for online event registration. However, that code uses a profile.