fix: check for src before attempting to add popover

assets/js/popover.js

@@ -10,7 +10,9 @@ function initPopover(baseURL) {
   document.addEventListener("DOMContentLoaded", () => {
     fetchData.then(({ content }) => {
       const links = [...document.getElementsByClassName("internal-link")]
-      links.forEach(li => {
+      links
+        .filter(li => li.dataset.src)
+        .forEach(li => {
           const linkDest = content[li.dataset.src.replace(basePath, "")]
           if (linkDest) {
             const popoverElement = `<div class="popover">