Bug 4.0.0-preview: NullReferenceException when TargetingContext.UserId is null and TargetingEvaluationOption.IgnoreCase = true

[zhiyuanliang-ms]

https://github.com/microsoft/FeatureManagement-Dotnet/blob/preview/src/Microsoft.FeatureManagement/Targeting/TargetingEvaluator.cs#L283

targetingContext.UserId can be null.