Add null contitional operator to installers.installer.InstallerType

[TheShadowEevee]

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  WingetCreate Crashes #466 - Noticed separate from this issue, but found when looking for existing issues

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• Adds a Null Conditional Operator to installers.installer.InstallerType.
  • InstallerType is a required field, but is not always defined in the installer list. It may be defined for all lists earlier in the schema, so it should be potentially null here.

Additionally tested against NoMachine.NoMachine (The package I noticed this on) and Microsoft.WindowsSDK.10.0.22621 (The package from #466).

Below screenshots were generated by:

• Running wingetcreate.exe update Microsoft.WindowsSDK.10.0.22621 -i
• Feeding in the same Installer URL
• Responding n then y to keep the manifest and edit it
• Selecting INSTALLER manifest
• Selecting Installers property
• Observing Crash vs No Crash

Microsoft.WindowsSDK.10.0.22621 before this change:

Microsoft.WindowsSDK.10.0.22621 after this change:

Microsoft Reviewers: Open in CodeFlow

[yao-msft]

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