Fix unquoted HTML attributes (closes #1484190)

program/steps/mail/func.inc

@@ -1252,6 +1252,7 @@ function rcmail_mod_html_body($body, $container_id)
 // parse link attributes and set correct target
 function rcmail_alter_html_link($in)
   {
+  $in = preg_replace('/=([^("|\s)]+)(\s|$)/', '="\1"', $in);
   $attrib = parse_attrib_string($in);
 
   if (stristr((string)$attrib['href'], 'mailto:'))