Wait until first observation to initially hide overlapped sidebars

A url that scrolls the page to an overlapping region would not hide the sidebar properly since the elements were not yet observed.

(e.g. https://quarto.org/docs/authoring/article-layout.html#margin-references)

Author: dragonstyle

src/resources/formats/html/quarto.js

@@ -531,6 +531,7 @@ window.document.addEventListener("DOMContentLoaded", function (_event) {
     });
   }
 
+  let hasObserved = false;
   const visibleItemObserver = (els) => {
     let visibleElements = [];
     const intersectionObserver = new IntersectionObserver(
@@ -546,6 +547,11 @@ window.document.addEventListener("DOMContentLoaded", function (_event) {
             });
           }
         });
+
+        if (!hasObserved) {
+          hideOverlappedSidebars();
+        }
+        hasObserved = true;
       },
       {}
     );
@@ -600,7 +606,6 @@ window.document.addEventListener("DOMContentLoaded", function (_event) {
       slowTransition(readerMode);
     }
     highlightReaderToggle(readerMode);
-    hideOverlappedSidebars();
 
     // If we're exiting reader mode, restore the non-slow transition
     if (!readerMode) {