fix combined/three panel transition to expandable mode

js/Article.js

@@ -282,7 +282,11 @@ const Article = {
 			console.log("packing", row.id);
 			row.setAttribute("data-is-packed", "1");
 
-			row.querySelector(".content-inner").innerHTML = `<div class="text-center text-muted">
+			const content_inner = row.querySelector(".content-inner");
+
+			// missing in unexpanded mode
+			if (content_inner)
+				content_inner.innerHTML = `<div class="text-center text-muted">
 					${__("Loading, please wait...")}
 				</div>`
 		}