wrong use of strip_tags

`        $mail_content_plain = $this->generate_message_plain (implode("\r\n", strip_tags(str_replace("<br>","\n",$body))));`
should be
`        $mail_content_plain = $this->generate_message_plain (strip_tags(implode("\r\n", str_replace("<br>","\n",$body))));
`
as strip_tags needs a string, str_replace returns in this case an array