Ensure usertoname gets initialised in email_user (bug #515497)

Signed-off-by: Richard Mansfield <richardm@catalyst.net.nz>

htdocs/lang/en.utf8/mahara.php

@@ -433,6 +433,7 @@ $string['noinstitutionsetpassemailmessagehtml'] = '<p>Dear %s,</p>
 
 <p><a href="%sforgotpass.php?key=%s">%sforgotpass.php?key=%s</a></p>';
 $string['debugemail'] = 'NOTICE: This e-mail was intended for %s <%s> but has been sent to you as per the "sendallemailto" configuration setting.';
+$string['divertingemailto'] = 'Diverting email to %s';
 
 
 // Expiry times

htdocs/lib/user.php

@@ -389,6 +389,7 @@ function email_user($userto, $userfrom, $subject, $messagetext, $messagehtml='',
         if ($messagehtml) {
             $messagehtml = '<p>' . hsc($notice) . '</p>' . $messagehtml;
         }
+        $usertoname = display_name($userto, $userto, true) . ' (' . get_string('divertingemailto', 'mahara', $to) . ')';
     }
     else {
         $usertoname = display_name($userto, $userto);