libstagefright: Fix to free buffers in error scenarios

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

Change-Id: Icdee687dab4883639f49ba0b38d6c80d7013873b