Crun incorrectly parses `crun exec` option `-u`, leading to privilege escalation

crun is an open source OCI Container Runtime fully written in C. In versions 1.19 through 1.26, the `crun exec` option `-u` (`--user`) is incorrectly parsed. The value `1` is interpreted as UID 0 and GID 0 when it should have been UID 1 and GID 0. The process thus runs with higher privileges than expected. Version 1.27 patches the issue.