Replace deprecated defaults() calls by a combination of ?? and ?: operators in mod/

mod/wallmessage.php

@@ -131,8 +131,8 @@ function wallmessage_content(App $a) {
 		'$subject'    => L10n::t('Subject:'),
 		'$recipname'  => $user['username'],
 		'$nickname'   => $user['nickname'],
-		'$subjtxt'    => defaults($_REQUEST, 'subject', ''),
-		'$text'       => defaults($_REQUEST, 'body', ''),
+		'$subjtxt'    => $_REQUEST['subject'] ?? '',
+		'$text'       => $_REQUEST['body'] ?? '',
 		'$readonly'   => '',
 		'$yourmessage'=> L10n::t('Your message:'),
 		'$parent'     => '',