commonmark_x reader with implicit_figures isn't checking whether the caption is empty?

[wlupton]

I think this is a bug in commonmark_x+implicit_figures (the caption is empty, so it should be an image, not a figure)? If agreed, I can create an issue. Thanks.

% pandoc -v
pandoc 3.5

% pandoc -f markdown <<<'![](Cat.png)'
<p><img src="Cat.png" /></p>

% pandoc -f commonmark_x+implicit_figures <<<'![](Cat.png)'
<figure>
<img src="Cat.png" />
<figcaption aria-hidden="true"></figcaption>
</figure>

[wlupton]

I created #10421.