Steps to reproduce the issue

Generate an email by sending a private message to your super admin (Like when an Information Request is confirmed by a user in Joomla 3.9)

Expected result

As this is a plain text email that is sent, the url with valid ampersands should have & and not &

Actual result

Please log in to http://0.0.0.0/administrator/index.php?option=com_messages&view=message&message_id=4 to read your message.

full source of email including headers

Content-Type: text/plain; charset=utf-8
Date: Fri, 19 Oct 2018 00:20:09 +0000
From: joomla-cms <phil@phil-taylor.com>
MIME-Version: 1.0
Message-ID: <e9192cb0adeef8dbc5a97526b588ce18@0.0.0.0>
Received: from 0.0.0.0 by mailhog.example (MailHog)
          id 5MOsywPV_l9FPMiQnJnMIk4WXZ-bktRQZwn9ai3Wm_Y=@mailhog.example; Fri, 19 Oct 2018 00:20:09 +0000
Reply-To: Super User <phil@phil-taylor.com>
Return-Path: <phil@phil-taylor.com>
Subject: New Message from Super User at joomla-cms
To: Super User <phil@phil-taylor.com>

Information Request Confirmed By User

User phil@phil-taylor.com has confirmed their information request.

Please log in to http://0.0.0.0/administrator/index.php?option=com_messages&amp;view=message&amp;message_id=4 to read your message.