semodule-utils: fix comparison with argc

In order for argv[3] to be used, argc needs to be at least 4, not 3.

This bug was found using lgtm.com analyzer:
https://lgtm.com/projects/g/fishilico/selinux-for-lgtm/snapshot/8c1b2658f80392ff8b3532c6bd5d0cefac8afb30/files/semodule-utils/semodule_package/semodule_unpackage.c?sort=name&dir=ASC&mode=heatmap#xb1ce80b43260d34c:1

Signed-off-by: Nicolas Iooss <nicolas.iooss@m4x.org>
1 file changed