Audio HAL VTS: stopped stream state getters may return INVALID_STATE

A never started stream should have its render position and next write
timestamp at 0 or indicate that the state is invalid.

Test: vts-tradefed run vts --module VtsHalAudioV2_0Target
Test: call/play music/record/video...
Bug: 36311550
Change-Id: I62e16066bb22101ee8f75154fc6c85a66be2f402
Signed-off-by: Kevin Rocard <krocard@google.com>