FIX 'NoneType' object has no attribute 'isalpha' (#2440)

passerbya

2025-03-20 5ee2f382b32c5c0beaa1c133b466a100c6fb7ebc

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ID0012W0013 https://isv-data.oss-cn-hangzhou.aliyuncs.com/ics/MaaS/ASR/test_audio/asr_example_zh.wav
ID0012W0014 https://isv-data.oss-cn-hangzhou.aliyuncs.com/ics/MaaS/ASR/test_audio/asr_example_en.wav