return if no page.latest (#303)

Patches v0.29.0, which introduced a bug that resulted in an Antora FATAL when trying to calcalute the canonical URL value if no `page.latest` value exists for a page.

Author: recrwplay

src/helpers/neo-canonical-current.js

@@ -7,6 +7,7 @@
 'use strict'
 
 module.exports = (page) => {
+  if (!page.latest) return page.canonicalUrl
   const re = new RegExp(`/${page.latest.version}/`)
   const latestVersionPath = `/${(page.attributes['latest-version-path'] || 'current')}/`
   return page.canonicalUrl.replace(re, latestVersionPath)