fix: do not remove Edit on GitHub if it does not exist (#4739)

Do not attempt to remove #editOnGitHubLink's .parentNode if it doesn't exist on the page.
For example, this element does not exist on 404 page: https://nodejs.org/amNotExist

Author: LiviaMedeiros

static/js/main.js

@@ -166,6 +166,10 @@
   var editOnGitHubElement = document.getElementById('editOnGitHubLink');
   var editOnGitHubUrlElement = document.getElementById('editOnGitHubUrl');
 
+  if (!editOnGitHubElement) {
+    return;
+  }
+
   if (editOnGitHubUrlElement) {
     editOnGitHubElement.setAttribute('href', editOnGitHubUrlElement.value);
   } else {