Fix strictmode error logs due to task snapshot hw buffer not being closed

- Wrapping the buffer into a bitmap will add a reference so we can
  close the buffer once we convert the TaskSnapshot into a
  ThumbnailData
- Also probably shouldn't be creating a new ThumbnailData for each
  local task stack listener (most of whom don't actually handle this
  method)

Fixes: 165825625
Test: Check logs
Change-Id: I4d881721692a960ac40be848e49188afddbbc9c3