Camera2/3: As a fallback, unilaterally free old recording buffers

When starting a recording session, check for and clear out recording
buffers still owned by stagefright from a previous recording session,
if any.  There should never be any, but in case they are due to a bug
elsewhere in the system, clearing out the buffers makes recovery
possible.

Bug: 9591080
Change-Id: I3a2a1256860bd174381cd525948419f985c9b415