Index out of bounds on FeatureManager.GetFeatureNames when flags array is empty

[esotuvaka]

This code:

func (fm *FeatureManager) GetFeatureNames() []string {
	flags, err := fm.featureProvider.GetFeatureFlags()
	if err != nil {
		log.Printf("failed to get feature flag names: %v", err)
		return nil
	}

	res := make([]string, 0, len(flags))
	for i, flag := range flags {
		res[i] = flag.ID
	}

	return res
}

Will index OOB if flags returns an empty []string. This causes a panic in client code that calls into this SDK