Issue #3376862: Preview keeps on reopening after closing

js/same-page-preview.js

@@ -68,6 +68,12 @@
 
     // Force a refresh of the preview pane.
     forceRefresh: async () => {
+      // If no preview iframe already open, nothing to do.
+      const iframe = document.querySelector('iframe.preview');
+      if (!iframe) {
+        return;
+      }
+
       if (defaultPreviewBtn) {
         const iframe = document.querySelector(samePagePreviewPane);
         const iframeWindow = iframe?.contentWindow;