(dev/mail#41) "Preview as HTML" - Fix error with tracking urls

[seamuslee001]

Overview

Fix regression in email preview. Use-case:

• Compose a "Mailing => New Mailing"
• Fill in basic in fields.
• In the body of the mailing, include a hyperlink
• Press the button "Preview as HTML"

This is an alternate version to #13813 based on Monish's comment at #13813 (comment)

Before

Fatal error generating trying to preview mailing

After

Preview works

ping @monishdeb @eileenmcnaughton @scardinius

[civibot]

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[lcdservices]

I tested this and confirmed it fixes the issue. This should probably be considered for a dot release, or at least the 5.13.0 release, as it's clearly a regression.

[seamuslee001]

i've put this against 5.13 now based on Brian's comment ping @eileenmcnaughton @mattwire @monishdeb

[colemanw]

This change looks good to me. Tagging merge-on-pass based on my code review and Brian's testing.
@seamuslee001 I'd also be happy to consider this for 5.12.2

[eileenmcnaughton]

unrelated fail