Video seeking not working

[restlessmodem]

Hi,
I noticed on my dockerized seafile instance that seeking does not work for uploaded videos.
This is related to not sending the "Accept-Ranges" HTTP header.

I worked around this issue and drastically improved video streaming perfomance by adding
proxy_force_ranges on;
to the seafile.nginx.conf inside the container.

Alternativly seafhttp could send the "Accept-Ranges" header and nginx should relay it.

The instance demo.seafile.com seems to be configured correctly.