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fix

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修复：EnableSkipDecoder 开关在 Buffer 协议场景下不生效

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en:
In the Buffer scenario, dataLen will be negative. unmarshalThriftData doesn't take this into account, leading to the logic even if SkipDecoder is not turned on.
zh(optional):
在 Buffer 场景下， dataLen 会为负数，unmarshalThriftData 没有考虑到这种情况导致即使 SkipDecoder 没有开启也会走到相关逻辑

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