Add empty or invalid configuration message

[FabienTschanz]

Pull Request (PR) description

This PR adds a message about an empty parsed content from ConvertTo-DSCObject in Initialize-M365DSCReporting. This is done to improve error visibility when a comparison against an empty or invalid configuration is done, where ConvertTo-DSCObject returns a $null object.

There is also a PR open at the DSCParser repository which outputs the errors during parse: microsoft/DSCParser#59

This Pull Request (PR) fixes the following issues

• Fixes Compare-M365DSCConfigurations: Export produces configurations that cannot be compared #5658

Task list

• Added an entry to the change log under the Unreleased section of the file CHANGELOG.md.
  Entry should say what was changed and how that affects users (if applicable), and
  reference the issue being resolved (if applicable).
• Resource parameter descriptions added/updated in the schema.mof.
• Resource documentation added/updated in README.md.
• Resource settings.json file contains all required permissions.
• Examples appropriately added/updated.
• Unit tests added/updated.
• New/changed code adheres to DSC Community Style Guidelines.