Fix prefix concatenation in timestamp post-processing for sensevoice (#2670)

slin000111

2025-09-20 88b464edb94531ba98744a5338965af539ab18ec

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BAC009S0764W0121 <|NEUTRAL|>
BAC009S0916W0489 <|NEUTRAL|>
asr_example_cn_en <|NEUTRAL|>
ID0012W0014 <|NEUTRAL|>