be more defensive when matching for section highlight

Author: splitbrain

lib/scripts/page.js

@@ -26,7 +26,9 @@ dw_page = {
              */
             .each(function () {
                 let $tgt = jQuery(this).parent();
-                const nr = $tgt.attr('class').match(/(\s+|^)editbutton_(\d+)(\s+|$)/)[2];
+                const match = $tgt.attr('class').match(/(\s+|^)editbutton_(\d+)(\s+|$)/);
+                if(!match) return;
+                const nr = match[2];
                 let $highlight = jQuery(); // holder for elements in the section to be highlighted
                 const $highlightWrap = jQuery('<div class="section_highlight_wrapper"></div>');