NuPlayer : Fix incorrect timestamp update for offload playback

- Progress bar keeps moving post offload audio tear down
- Pause start time is reset during session tear down causing the issue
- Fix the issue by resetting only when
  clip is not offloaded OR not paused

Change-Id: I4c7632dab1dddc73781e13cbf93b52afb4166c34
CRs-Fixed: 765524