Validate the previous overlay and bypass handles before unlocking
the buffers. The reason for doing this, is that in certain use cases,
after the previous handles are stored, the buffer gets destroyed and the
handle is now invalid. The HWC however doesn't know that the handle is
invalid and tries to unlock the handle, resulting in a failure.
CRs-fixed: 323614
Change-Id: I0f0c8506e7e22f9fc01eb28af0270f9c4587c787
8287f5bbcb