reg/select-domain.inc.php: fix operator precedence

pg-view/reg/select-domain.inc.php

@@ -7,6 +7,6 @@ $user_domains = regListUserDomains();
 if (!in_array($_POST['domain'] ?? NULL, $user_domains, true))
 	echo '		<option value="" disabled="" selected="">—</option>' . LF;
 foreach ($user_domains as $domain)
-	echo '		<option value="' . $domain . '"' . (($_POST['domain'] ?? NULL === $domain) ? ' selected=""' : '') . '>' . $domain . '</option>' . LF;
+	echo '		<option value="' . $domain . '"' . ((($_POST['domain'] ?? NULL) === $domain) ? ' selected=""' : '') . '>' . $domain . '</option>' . LF;
 ?>
 	</select>