Validation step optimization

allows for exiting the loop early on match

Co-authored-by: Emil Lundberg <emil@yubico.com>

index.bs

@@ -4121,8 +4121,10 @@ To validate the calling origin is an authorized related origin for a given cerem
     1. Let |domain| be the [=effective domain=] of |url|. If that is null, [=continue=].
     1. Remove any [=public suffix=] from the end of |domain|, including private registries and unknown registries. If |domain| is now empty, [=continue=].
     1. Split |domain| into [=origin labels|labels=] and let |label| be the right-most one.
-    1. If |label| is not in |labelsSeen| and the number of elements in |labelsSeen| is less than |maxLabels|, then insert |label| into |labelsSeen|. Otherwise, [=continue=]. 
+    1. If |labelsSeen| [=set/contains=] |label|, [=continue=].
     1. If |rpIdRequested| and |url| are [=same origin=], return `true`.
+    1. [=set/Append=] |label| to |labelsSeen|.
+    1. If the [=set/size=] of |labelsSeen| is greater than or equal to |maxLabels|, [=break=].
 1. Return `false`.
 
 # WebAuthn <dfn>Authenticator Model</dfn> # {#sctn-authenticator-model}