reader: avoid gcc warning
reader: avoid gcc warning

gcc warns that r might be uninitialized, because it doesn't
know that r will be initialized in the 'if' statement.

Initialize the variable to avoid the warning.

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