Spamspan displays last anchor attribute if no text is given

Problem/Motivation

If we use anchor tags without text content or simply an icon, the last attribute of the anchor tag / icon will be rendered as its content instead!

Steps to reproduce

• Use the filter format on an anchor tag structured as follows:

<a href="mailto:example@email.com"></a>

or

<a href="mailto:example@email.com">
  <i class="my-icon"></i>
</a>

• The anchor tag will be broken

Proposed resolution

Remaining tasks

User interface changes

API changes

Data model changes