libstagefright: Fix to free buffers in error scenarios

- MediaBuffer objects are not freed if component transitions from
  IDLE->EXECUTING or EXECUTING->LOADED fails (or if the
  OMX_CmdComplete messages are dropped due to an earlier error)
  Additionally with native buffers, the corresponding
  ANativeWindowBuffers are not cancelled back in the above scenarios.

CRs-Fixed: 640236

Change-Id: I62bdcde5d52ee65cba457a9b5e938e0390d8d9b4