Fix middleware on initial load without loaders

Author: brophdawg11

.changeset/twelve-dogs-pump.md

@@ -0,0 +1,5 @@
+---
+"react-router": patch
+---
+
+Fix Data Mode regression causing a 404 during initial load in when `middleware` exists without any `loader` functions

packages/react-router/lib/router/router.ts

@@ -5751,6 +5751,19 @@ function getDataStrategyMatch(
           !isMutationMethod(request.method) &&
           (match.route.lazy || match.route.loader))
       ) {
+        // If this match was marked `shouldLoad` due to a middleware and it
+        // doesn't have a `loader` to run and no `lazy` to add one, then we can
+        // just return undefined from the "loader" here
+        if (
+          match.route.middleware &&
+          match.route.middleware.length > 0 &&
+          match.route.loader == null &&
+          !match.route.lazy &&
+          !handlerOverride
+        ) {
+          return Promise.resolve({ type: ResultType.data, result: undefined });
+        }
+
         return callLoaderOrAction({
           request,
           match,