tools,doc: fix version picker bug in html.js

The processing of strings like `8.x` into a major version number and a
minor version number results in minor versions that are `NaN`. In that
situation, since the picker will link to the latest docs in the
major version, include the version in the version picker.

Fixes: https://github.com/nodejs/node/issues/23979
PR-URL: https://github.com/nodejs/node/pull/24638


Reviewed-By: Vse Mozhet Byt <vsemozhetbyt@gmail.com>
Reviewed-By: Ruben Bridgewater <ruben@bridgewater.de>
Reviewed-By: Refael Ackermann <refack@gmail.com>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: Franziska Hinkelmann <franziska.hinkelmann@gmail.com>