Security Snapshot May Use Unintended Timestamp When Only ISAR_APT_SNAPSHOT_DATE Is Set

Isar is an integration system for automated root filesystem generation. In versions 0.11-rc1 and 0.11, defining ISAR_APT_SNAPSHOT_DATE alone does not set the correct timestamp value for security distribution, leading to missed security updates. This issue has been patched via commit 738bcbb.