Fix infinite Loading progress on React 19 (#599)

* Fix infinite Loading progress on React 19

Closes issue #598- Fix infinite Loading progress on React 19

* use JSX

Co-authored-by: Kévin Dunglas <kevin@dunglas.fr>

* cs

---------

Co-authored-by: Kévin Dunglas <kevin@dunglas.fr>
Co-authored-by: soyuka <soyuka@users.noreply.github.com>

Author: 3 people

src/core/AdminGuesser.tsx

@@ -1,6 +1,7 @@
 import React, { useEffect, useMemo, useState } from 'react';
 import {
   AdminContext,
+  Loading,
   defaultI18nProvider,
   /* tree-shaking no-side-effects-when-called */ localStorageStore,
 } from 'react-admin';
@@ -95,6 +96,10 @@ const AdminGuesser = ({
     [setLoading, setIntrospect],
   );
 
+  if (loading) {
+    return <Loading />;
+  }
+
   return (
     <AdminContext
       i18nProvider={i18nProvider}