restore wrongly deleted code

Author: slorber

packages/docusaurus-theme-classic/src/theme/DocSidebarItem/Category/index.tsx

@@ -59,6 +59,9 @@ function useCategoryHrefWithSSRFallback(
 ): string | undefined {
   const isBrowser = useIsBrowser();
   return useMemo(() => {
+    if (item.href && !item.linkUnlisted) {
+      return item.href;
+    }
     // In these cases, it's not necessary to render a fallback
     // We skip the "findFirstCategoryLink" computation
     if (isBrowser || !item.collapsible) {