sysdeps-unix: check fd before calling _dbus_fd_set_close_on_exec()
If /proc/self/oom_score_adj does not exist, fd will invalid (-1). Attempting to set the CLOEXEC flag will obviously fail, and we lose the original errno value from open().
Bug: https://bugs.gentoo.org/834725 Signed-off-by: Mike Gilbert floppym@gentoo.org
Fixup for !255 (merged)