systemd-python: add _Reader.closed attribute
systemd-python: add _Reader.closed attribute

This should make the file interface of _Reader complete.

keszybz/python-systemd,again4you/python-systemd,again4you/python-systemd,keszybz/python-systemd,Awesense/python-systemd,systemd/python-systemd,Awesense/python-systemd,Awesense/python-systemd,systemd/python-systemd