logger: fix -i argument parsing regression

logger: fix -i argument parsing regression

With earlier logger it's possible to combine the option -i with other
options, such as -s.  But currently:

$:~> logger -is
logger: failed to parse id: 's'

The changed behaviour breaks existing scripts like dhcpcd-run-hooks from
dhcpcd.

Broken-since: aab5b44405b9a6ada92e419e5a84cc0d1d4afee9
Reference: http://comments.gmane.org/gmane.linux.utilities.util-linux-ng/9683
Reported-by: Juergen Daubert <jue@jue.li>
Reviewed-by: Benno Schulenberg <bensberg@justemail.net>
Signed-off-by: Sami Kerola <kerolasa@iki.fi>