don't create duplicate contacts when sending test emails

[MegaphoneJon]

Overview

Sending test emails to contacts who have an email but shouldn't receive email (by virtual of having the "do not mail", "opt out", or "is deceased" flags) creates a duplicate contact.

You can replicate this by sending a test email to a contact with one of the above flags set.

Before

Duplicate contacts created.

After

No duplicate created. "No recipients found" warning is updated to account for this scenario.

[civibot]

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