DB Log error when Postmark API missing or incorrect

Problem/Motivation

If the Postmark API key is missing or wrong and an attempt is made to send an email, then Postmark generates an exception "PostmarkException" that contains the message

Unauthorized: Missing or incorrect API token in header. Please verify that you used the correct token when you constructed your client.

The entry posted to the DB log has

     $this->logger->error('Postmark exception occurred while trying to send email from %from to %to. @code: @message',
        [
          '%from' => $sender_signature,
          '%to' => $params['to'],
          '@code' => $e->postmarkApiErrorCode,
          '@message' => $e->message,
        ]

but the value $e->postmarkApiErrorCode is NULL. This causes Html::escape() to throw a TypeError when the dblog view renders the entry

Steps to reproduce

Load an invalid API key and send a test message, then check the DB log.

Proposed resolution

Update the log call to read:

      $this->logger->error('Postmark exception occurred while trying to send email from %from to %to. @code: @message',
        [
          '%from' => $sender_signature,
          '%to' => $params['to'],
          '@code' => $e->postmarkApiErrorCode ?? '',
          '@message' => $e->message ?? '',
        ]