Fix printing badges with malformed HTML

[OmeGak]

This fix handles both plain text and rich markdown elements. It's not perfect, as it strips unclosed tags, but at least it doesn't trigger an unhandled exception. These are examples of how different content is rendered in the badge.

Plain text input elements:

content	rendering
<x	<x
<x foo

Rich markdown input elements:

content	rendering
<x
<span sytle="color: red;">foo</span>	foo