0.4.x: Fix markdown rendering logic

[martinRenou]

Using the following code:

from ipywidgets import Output

from IPython.display import display, Markdown

out = Output()

with out:
    display(Markdown("[google](https://google.com)"))

out

Results in not rendering the link properly, instead we see the raw code inlined "[google](https://google.com)"

This PR is an attempt to fix that issue.

It turns out those changes are working for me 15% of the time... When it does not render, I see this:

Javascript Error: Loading chunk 8586 failed.
(error: https://cdnjs.cloudflare.com/ajax/libs/mathjax/2.7.7/extensions/8586.voila.js)

[github-actions]

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