resolve the index before rendering (#4806)

Co-authored-by: Evan Almloff <evanalmloff@gmail.com>

packages/fullstack-server/src/server.rs

@@ -284,9 +284,11 @@ impl RenderHandleState {
     ///     axum::serve(listener, router).await.unwrap();
     /// }
     /// ```
-    pub async fn render_handler(State(state): State<Self>, request: Request<Body>) -> Response {
+    pub async fn render_handler(State(mut state): State<Self>, request: Request<Body>) -> Response {
         let (parts, _) = request.into_parts();
 
+        state.config.resolve_index();
+
         let response = state
             .renderers
             .clone()