Support sound models with no data

This change allows using SoundModels with null or empty data.

Test: Manual testing of soundtrigger use-cases.
      Testing of null-/empty-data models using SoundTriggerTestService
      and mocked HAL.
Fixes: 181103994
Change-Id: I00b3c4e343a81e9f4f4580becf1128fd3ba60b14
4 files changed