Destroy the bz2 decompressor on destruction.

When the patching fails, we never close the decompressor which leaks
the internal decompressor structure. This patch keeps track of that and
releases it when needed.

Bug: chromium:820043
Test: Ran it through ASAN with the example provided in the bug before and after this patch.
Change-Id: I29d3e99608333c6b8bf129a89cba26b7d029a561