In
a3fcadddc871e646 sftp: close idle connections after --sftp-idle-timeout (1m by default)
Idle SFTP connections were closed after 1 minute. However due to the
way SSH multiplexes connections over a single SSH connection this
meant that if uploads or downloads went on for more than one minute
they failed with "EOF errors" as their underlying connection was
closed.
This fixes the problem by not clearing idle connections if there are
any transfers in progress.
Fixes#5197