VolumeShaper: Improve restore

Consider whether VolumeShaper has been started or not when
restoring (position). If the VolumeShaper hasn't been started
we restore in that state.  If it has been started already,
we advance to the end assuming the duration has been played out.

Test: CTS and headset / kill audioserver
Bug: 37536598
Change-Id: I4b55dca6f6a859563fd20bad4c8f67d2c92321c0