Special tags in welcome message breaks swagger file

[lmarini]

When using special tags in the admin > customize > welcome message the /swagger returns an invalid swagger file.

For example:

The Permafrost Discovery Gateway is an online platform for archiving, processing, analysis, and visualization of permafrost big imagery products to enable discovery and knowledge-generation.
<br><br>
For more information on the the Permafrost Discovery Gateway please see <a href="https://arcticdata.io/catalog/portals/permafrost/About"> https://arcticdata.io/catalog/portals/permafrost/About</a>.	```

[longshuicy]

released in 1.18.1