Href gets sanitized when the link is a keyword

[lshaowei18]

Describe the bug

In the email template, when you have the href as a keyword like <a href="{{protectedlink}}">link</a>, it gets sanitised into <a href>link</a>.

To Reproduce

Expected behavior
Should retain the keyword. This affects registered mail.

[lamkeewei]

Not sure if it's helpful but we also faced a similar issue when we were working on Telegram. xss-js was sanitising tg://... links values too. We overrode safeAttrValue to solve this. Can reference #467 and here.

[lshaowei18]

Nice, thanks! Just tried it out and it works :)

[lshaowei18]

Done through #551