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: nodejs#23979

test/doctool/test-doctool-html.js

@@ -95,6 +95,10 @@ const testData = [
     html: '<ol><li>fish</li><li>fish</li></ol>' +
       '<ul><li>Red fish</li><li>Blue fish</li></ul>',
   },
+  {
+    file: fixtures.path('altdocs.md'),
+    html: '<li><ahref="https://nodejs.org/docs/latest-v8.x/api/foo.html">8.x',
+  },
 ];
 
 const spaces = /\s/g;
@@ -117,7 +121,8 @@ testData.forEach(({ file, html }) => {
         const actual = output.replace(spaces, '');
         // Assert that the input stripped of all whitespace contains the
         // expected markup.
-        assert(actual.includes(expected));
+        assert(actual.includes(expected),
+               `ACTUAL: ${actual}\nEXPECTED: ${expected}`);
       })
     );
   }));

test/fixtures/altdocs.md

@@ -0,0 +1,3 @@
+# ALTDOCS
+<!--introduced_in=v8.4.0-->
+

tools/doc/html.js

@@ -427,6 +427,7 @@ function altDocs(filename, docCreated) {
     const [versionMajor, versionMinor] = version.num.split('.').map(Number);
     if (docCreatedMajor > versionMajor) return false;
     if (docCreatedMajor < versionMajor) return true;
+    if (Number.isNaN(versionMinor)) return true;
     return docCreatedMinor <= versionMinor;
   }