Fix for types derived from un-namespaced types.

[DmitriySft]

Type.Namespace can be null. There are cases where such cases are not correctly handled.

The easiest example is:

interface INoNamespaceInterface { }
namespace MyNamespace
{
    public class MyType: INoNamespaceInterface {} // Gives NRE
}

This PR fixes this problem.

But codebase-wise, there are places where Type.Namespace == null is not handled well. Suggest to fix all of them together with this feature request #262

[DmitriySft]

@microsoft-github-policy-service agree

[jasongin]

Thanks for the PR and bug report.

It looks like the CI is just complaining about some pedantic issues in the test code. For info about that check see https://github.com/microsoft/node-api-dotnet/blob/main/README-DEV.md#checkfix-formatting

Since it's test code, it would be OK to disable some of those warnings with #pragma warning disable