DO NOT MERGE omx: check buffer port before using

Bug: 28816827
Change-Id: I3d5bad4a1ef96dec544b05bb31cc6f7109aae0a5

    BufferMeta(size_t size)
    BufferMeta(size_t size, OMX_U32 portIndex)
         : mSize(size),
          mIsBackup(false),
          mPortIndex(portIndex) {
     }

    BufferMeta(size_t size)
         : mSize(size),
          mIsBackup(false) {
     }
