An empty <pre> tag will break the read-only site

[peterbe]

Summary

If the document contains the string <pre></pre> it will break the rendering on the read-only site.

Steps To Reproduce (STR)

1. Edit a wiki page and in the source put in <pre></pre>
2. Save
3. View on the read-only domain

Actual behavior

Expected behavior

Not to crash.

Additional context

Here's the code that assumes that there's always >=1 childNodes

[peterbe]

I created this: https://developer.allizom.org/en-US/docs/Web/SVG/Element/feTurbulence