fix #2587: Resolve VAD multithreading issue (#2613)

* Fix crash in ASR tasks when lm is set to none in #2237

* fix #2587: Resolve VAD multithreading issue

* Update funasr/models/fsmn_vad_streaming/model.py

ok

Co-authored-by: gemini-code-assist[bot] <176961590+gemini-code-assist[bot]@users.noreply.github.com>

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Co-authored-by: gemini-code-assist[bot] <176961590+gemini-code-assist[bot]@users.noreply.github.com>