Ensure checksums are always defined when requested

[Thilas]

Description Of Changes

Throws an error in case a requested checksum is missing.

Motivation and Context

I don't really understand why but using AU, I ended once having no checksums even though they are usually always automatically calculated by AU.

This change is meant to catch this issue as early as possible.

Testing

N/A

Operating Systems Testing

• Windows 11
• Windows Server 2022

Change Types Made

• Bug fix (non-breaking change).
• Feature / Enhancement (non-breaking change).
• Breaking change (fix or feature that could cause existing functionality to change).
• Documentation changes.
• PowerShell code changes.

Change Checklist

• Requires a change to the documentation.
• Documentation has been updated.
• Tests to cover my changes, have been added.
• All new and existing tests passed?
• PowerShell code changes: PowerShell v2 compatibility checked?

Related Issue

Supersedes #30