fix: lesson content rendering

frontend/src/pages/Lesson.vue

@@ -237,6 +237,8 @@ const lesson = createResource({
 
 const renderEditor = (holder, content) => {
 	// empty the holder
+	if (document.getElementById(holder))
+		document.getElementById(holder).innerHTML = ''
 	return new EditorJS({
 		holder: holder,
 		tools: getEditorTools(),