Bugfix: Fix sporadic stream reset between rclone and restic

Sometimes when using restic with the rclone backend, an error message similar to the following is printed:

    Didn't finish writing GET request (wrote 0/xxx): http2: stream closed

It was found that this is caused by restic closing the connection to rclone
when downloading data too fast. A workaround was added which waits for the end
of the download before closing the connection.

https://github.com/restic/restic/pull/3014
https://github.com/rclone/rclone/issues/2598