No address step before signing in when there's only one mail server

The server's own page asks for the username, so with a single server the
sign-in page keeps only the own-device choice. With several servers the
address still comes first, since its domain picks the server. One new string,
in all nine catalogues.

web/src/locales/nl.ts

@@ -1214,6 +1214,7 @@ export const catalog: Catalog = {
     "Could not send the receipt: {error}": "De leesbevestiging kon niet worden verzonden: {error}",
     "Could not sign in.": "Aanmelden mislukt.",
     "You'll enter your password on your mail server's sign-in page.": "U voert uw wachtwoord in op de aanmeldpagina van uw mailserver.",
+    "You'll sign in on your mail server's own page.": "U meldt zich aan op de eigen pagina van uw mailserver.",
     "This sign-in didn't start in this browser. Try again.": "Deze aanmelding is niet in deze browser begonnen. Probeer het opnieuw.",
     "The sign-in took too long. Try again.": "Het aanmelden duurde te lang. Probeer het opnieuw.",
     "Sign-in was cancelled.": "Het aanmelden is geannuleerd.",