Close TaskSnapshot's hardware buffer once no more strong reference to it.

After TaskSnapshot object being removed from cache, finished in persist
thread, and broadcast onSnapshotChange has done, close it's hardware
buffer, to ensure the hardware buffer being closed ASA no more
reference.

Bug: 238206323
Test: monkey
Change-Id: Id5f1b61b1e323fa1741c9482cd4f8e818f05b874