Fix markdown-in-html not always splitting HTML tags into separate lines (#558)

[Crozzers]

This PR fixes #558, which is a continuation from #546.

The issue is regarding markdown-in-html tags that are not on their own line. This issue was partially fixed in #547, but the solution was gated behind a check for if len(lines) < 3.
This check was based on the assumption that the snippets would look like this:

<div markdown="1">Some **text**
</div>

This assumption completely breaks down for longer snippets, leading to HTML tags not being properly split from the surrounding markdown.

This PR fixes this by always attempting to split the HTML tags into separate lines

[nicholasserra]

Thanks!