systemd-python: fix gcc warning
systemd-python: fix gcc warning

src/python-systemd/_reader.c: In function Reader_get_catalog:
src/python-systemd/_reader.c:912:53: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
             assert(mid_len > l);
                            ^

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