Fix two bugs for blank voice (empty speech): (#1403)

jianganghan

2024-02-29 f272eb4ef78e12a1ef4ae451b114f980a2682d51

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wget https://isv-data.oss-cn-hangzhou.aliyuncs.com/ics/MaaS/ASR/dep_libs/ffmpeg-N-111383-g20b8688092-linux64-gpl-shared.tar.xz
tar -xvf ffmpeg-N-111383-g20b8688092-linux64-gpl-shared.tar.xz