Bugfix for HTML Email Templates plugin

This plugin generates an HTML page which then becomes the email body. If the user's data is available, the page title will be like "Message from Jason Bourne". If the user's data is not available, the page title will be simply "Message from". Nobody usually sees this page title, since they're looking at it in a mail client rather than in an a browser, but it' still an unexpected behavior. Amending line 903 as follows fixes this. Thanks.

'{FROM_NAME}' => (($display_name)?$display_name:$blog_name),