Make the infrastructure TOC stuff robust against incorrect HTML.

layouts/partials/toc.html

@@ -18,9 +18,12 @@
                     {{ $current := $page.Scratch.Get "level" | int }}
 
                     {{ if gt $level $current }}
-                        <ul>
+                        {{ $delta := sub $level $current }}
+                        {{ range $index, $num := (seq $delta) }}
+                            <ul>
+                        {{ end }}
                     {{ else if lt $level $current }}
-                        {{ $delta := sub ($page.Scratch.Get "level") $level }}
+                        {{ $delta := sub $current $level }}
                         {{ range $index, $num := (seq $delta) }}
                             </ul>
                         {{ end }}

src/js/misc.js

@@ -488,7 +488,12 @@ function handlePageScroll() {
             var closestHeadingAboveTopPos = -1000000;
 
             for (var i = 0; i < tocLinks.length; i++) {
-                var cbr = tocHeadings[i].getBoundingClientRect();
+                var heading = tocHeadings[i];
+                if (heading === null) {
+                    continue;
+                }
+
+                var cbr = heading.getBoundingClientRect();
 
                 if (cbr.width || cbr.height) {
                     if ((cbr.top >= 0) && (cbr.top < window.innerHeight)) {