Scroll participant list to top on token change
Scroll participant list to top on token change

When switching conversations, the participant list's scroll container is
scrolled back to the top instead of keeping an arbitrary position.

Signed-off-by: Vincent Petry <87e1f221a672a14a323e57bb65eaea19d3ed3804@nextcloud.com>

nextcloud/spreed,nextcloud/spreed,nextcloud/spreed