大佬，帮忙解决下 VideoEncoderCore 中的todo吧，太容易crash了

[JesseWo]

if (mMuxer != null) {
            // TODO: stop() throws an exception if you haven't fed it any data.  Keep track
            //       of frames submitted, and don't call stop() if we haven't written anything.
            mMuxer.stop();
            mMuxer.release();
            mMuxer = null;
        }