Fix:max_tokens must be at least 1, got -950, BadRequestError (#10252)

### What problem does this PR solve?
https://github.com/infiniflow/ragflow/issues/10235

### Type of change

- [x] Bug Fix (non-breaking change which fixes an issue)
- [x] Refactoring

rag/llm/chat_model.py

@@ -870,6 +870,7 @@ class MistralChat(Base):
         return gen_conf
 
     def _chat(self, history, gen_conf={}, **kwargs):
+        gen_conf = self._clean_conf(gen_conf)
         response = self.client.chat(model=self.model_name, messages=history, **gen_conf)
         ans = response.choices[0].message.content
         if response.choices[0].finish_reason == "length":
@@ -882,9 +883,7 @@ class MistralChat(Base):
     def chat_streamly(self, system, history, gen_conf={}, **kwargs):
         if system and history and history[0].get("role") != "system":
             history.insert(0, {"role": "system", "content": system})
-        for k in list(gen_conf.keys()):
-            if k not in ["temperature", "top_p", "max_tokens"]:
-                del gen_conf[k]
+        gen_conf = self._clean_conf(gen_conf)
         ans = ""
         total_tokens = 0
         try: