Fix wrong anchors

While experimenting with the ToC changes, it became obvious that anchors
for those unnamed headers don't work.

This patch fixes those links by running the autolinkify twice and make
sure linkify only adds links to non-empty ids.

Signed-off-by: Sheogorath <sheogorath@shivering-isles.com>

public/js/extra.js

@@ -846,11 +846,13 @@ const linkifyAnchors = (level, containingElement) => {
     let header = headers[i]
     if (header.getElementsByClassName('anchor').length === 0) {
       if (typeof header.id === 'undefined' || header.id === '') {
-                // to escape characters not allow in css and humanize
+        // to escape characters not allow in css and humanize
         const id = slugifyWithUTF8(getHeaderContent(header))
         header.id = id
       }
-      header.insertBefore(anchorForId(header.id), header.firstChild)
+      if (!(typeof header.id === 'undefined' || header.id === '')) {
+        header.insertBefore(anchorForId(header.id), header.firstChild)
+      }
     }
   }
 }

public/js/index.js

@@ -2786,6 +2786,7 @@ function updateViewInner () {
   renderTOC(ui.area.markdown)
   generateToc('ui-toc')
   generateToc('ui-toc-affix')
+  autoLinkify(ui.area.markdown)
   generateScrollspy()
   updateScrollspy()
   smoothHashScroll()