Update error page

[ThibaudDauce]

• Add stacktrace for debug (should only be present in dev, I think… I hope…)
• Show nothing if there is no error (prevent the problem with showing a 500 on no errors for a brief time while navigating out of the page). See 😨 Affichage des pages d’erreur : 404 et erreurs génériques data.gouv.fr#1816 (comment)
• Fix a small bug when visiting a 404 dataset (cannot get ID from null). Maybe related to 500 error "Cannot read properties of null (reading 'id')" on 404 #695