renderTableHTML only fails on unsupported node kinds, which a parsed
<table> never triggers, so the degenerate flatten-children branch in
walkHTMLLeaf is unreachable. Remove it so the nested-table path matches
the top-level walkHTMLBlocks case (both skip silently when the markup is
empty).
Also tighten the inaccurate 'mirrors Python's HtmlParser' inline comment
in the same block (the two-item split is the markdown_parser.go model;
Python keeps the table once, outside the inline flow).