[Bug] 总结历史会话时，会有一条空的system 消息，导致 LM Studio 报错 about chatgpt-next-web

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Title: [Bug] When summarizing historical sessions, there will be an empty system message, causing LM Studio to report an error

[hossain666]

firefox-devtools/profiler#4988__

[hossain666]

[hossain666]

firefox-devtools/profiler#4988

[hossain666]

[] f4a9f2ca90cd026804f3a87ca52afc87a5966bc8()

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[hossain666]

@hossain666 f4a9f2ca90cd026804f3a87ca52afc87a5966bc8

[hossain666]

[] f4a9f2ca90cd026804f3a87ca52afc87a5966bc8()

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[Dean-YZG]

产生空系统消息的原因一般是：历史消息长度大于设定的压缩消息长度阈值 ，会发起一次对话，用于总结历史消息，同时携带上一次的『总结』，这样的方式来生成新的『总结』，作为新的『压缩消息』，但是，有时『上一次的总结』不存在，例如被清空，或是第一次发起『消息压缩』，这是逻辑默认增加一个空字符串作为『上一次总结』。这个pr兼容不支持空字符串的模型，将空字符串修改为";"
#4671

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The reason for generating empty system messages is generally that the length of historical messages is greater than the set compression message length threshold. A dialogue will be initiated to summarize historical messages and carry the last "summary". In this way, a new "summary" is generated. ”, as a new “compressed message”, however, sometimes the “last summary” does not exist, for example, it is cleared, or the “message compression” is initiated for the first time, this is the logical default to add an empty string as the “last summary” Summarize". This PR is compatible with models that do not support empty strings. Change the empty string to ";"
#4671