Allow exemption for VoiceRecognitionService if no VoiceInteraction

If there is no VoiceInteractionService set, allow the current
VoiceRecognitionService to be trusted. For example, when "Basic Google
Recognition" is selected in settings, for some assistant other than
Google, there is no Voice Interaction Service set

Test: manual
Bug: 162547999
Change-Id: I10385ee97d2ebc8597876cfd02168878720ad7e7