WS core_rating_get_item_ratings returns wrong avatar URLs

 Steps to reproduce

1. Create a forum and enable ratings with a numeric scale. Find the ID of the forum course module.
2. As a student, post to the forum and find the ID of the post.
3. As a teacher, set a profile image and rate the post of the student.
4. Create a web service token for the teacher.
5. Run (replacing the site URL,, course module id, post id and token):
   curl 'http://site_url/webservice/rest/server.php?moodlewsrestformat=json' --data 'contextlevel=module&instanceid=29&component=mod_forum&ratingarea=post&itemid=20&scaleid=5&sort=timemodified&moodlewssettingfilter=true&moodlewssettingfileurl=true&wsfunction=core_rating_get_item_ratings&wstoken=c89cffe18f9becf6479b392cef329ca8' | jq
6. Look at the "userpictureurl" field returned by the web service, the URL points to the wrong avatar . EXPECTED RESULT: the "userpictureurl" should return the avatar of the teacher.