Fix TOC TypeError when current section is null, and only update current class when there's a change (as LI will never equal H2/H3).

Author: jsantell

docs_js_css/toc.js

@@ -69,19 +69,21 @@ class TOC{
 if(top==TOC.lastTop)return;
 TOC.lastTop=top;
 
-letminDiff=1000000000,current=null;
+letminDiff=1000000000,currentId=null;
 for(letsectionofTOC.sections){
 letot=section.offsetTop-50;
 if(ot>top)continue;
 letdiff=top-ot;
 if(diff<minDiff){
 minDiff=diff;
-current=section;
+currentId=section.id;
 }
 }
-if(TOC.lastLi!=current){
+
+letcurrentLi=currentId ? document.querySelector(`#li_${currentId}`) : null;
+if(TOC.lastLi!=currentLi){
 if(TOC.lastLi!=null)TOC.lastLi.classList.remove('current');
-TOC.lastLi=document.getElementById('li_'+current.id);
+TOC.lastLi=currentLi||null;
 if(TOC.lastLi!=null)TOC.lastLi.classList.add('current');
 }
 }