Fix existing username validator not allowing multiple accounts (#16153)

Fix #16107

app/validators/existing_username_validator.rb

@@ -19,10 +19,10 @@ class ExistingUsernameValidator < ActiveModel::EachValidator
       str unless Account.find_remote(username, domain)
     end
 
-    if usernames_with_no_accounts.any? && options[:multiple]
+    if options[:multiple]
-      record.errors.add(attribute, I18n.t('existing_username_validator.not_found_multiple', usernames: usernames_with_no_accounts.join(', ')))
+      record.errors.add(attribute, I18n.t('existing_username_validator.not_found_multiple', usernames: usernames_with_no_accounts.join(', '))) if usernames_with_no_accounts.any?
-    elsif usernames_with_no_accounts.any? || usernames_and_domains.size > 1
+    else
-      record.errors.add(attribute, I18n.t('existing_username_validator.not_found'))
+      record.errors.add(attribute, I18n.t('existing_username_validator.not_found')) if usernames_with_no_accounts.any? || usernames_and_domains.size > 1
     end
   end
 end