Allow getCapturePosition to return 0 frames for unprepared streams

For device supporting getCapturePosition,
VTS only allowed unprepared stream to return INVALID_STATE.
Now also allow for the stream to return 0 frames similarly to the other
non started states.

Test: vts-tradefed run commandAndExit vts --module VtsHalAudioV2_0Target
Bug: 110367728
Cherry-piked from: d01dc3edac9e92981e7ae419d0e7622f753acf94
Change-Id: Ibdf8df8cb8809e98c40a50035371df6893fe4da4
Signed-off-by: Kevin Rocard <krocard@google.com>