book restore from moodle 1.9: Images are not imported

A linked or embedded image from the course_files in Moodle 1.9 is not converted when restoring a 1.9 backup in moodle 2.3.

Reason: https://github.com/moodle/moodle/blob/master/mod/book/backup/moodle1/lib.php

The moodle2-xml file is written before the images are migrated and so the @FILEPHP@ Links are not replaced by the @@PLUGINFILE@@ Links. $this->write_xml('chapter', $data, array('/chapter/id')); should be executed at the end.

public function process_book_chapters($data) {

    $this->write_xml('chapter', $data, array('/chapter/id'));

    // convert chapter files

    $this->fileman->filearea = 'chapter';

    $this->fileman->itemid   = $data['id'];

    $data['content'] = moodle1_converter::migrate_referenced_files($data['content'], $this->fileman);

}