Fix:disallowed special token while embedding (#8692)

### What problem does this PR solve?

https://github.com/infiniflow/ragflow/issues/8567

### Type of change

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

rag/llm/embedding_model.py

@@ -273,6 +273,8 @@ class ZhipuEmbed(Base):
 class OllamaEmbed(Base):
     _FACTORY_NAME = "Ollama"
 
+    _special_tokens = ["<|endoftext|>"]
+
     def __init__(self, key, model_name, **kwargs):
         self.client = Client(host=kwargs["base_url"]) if not key or key == "x" else Client(host=kwargs["base_url"], headers={"Authorization": f"Bear {key}"})
         self.model_name = model_name
@@ -281,6 +283,9 @@ class OllamaEmbed(Base):
         arr = []
         tks_num = 0
         for txt in texts:
+            # remove special tokens if they exist
+            for token in OllamaEmbed._special_tokens:
+                txt = txt.replace(token, "")
             res = self.client.embeddings(prompt=txt, model=self.model_name, options={"use_mmap": True})
             try:
                 arr.append(res["embedding"])
@@ -290,6 +295,9 @@ class OllamaEmbed(Base):
         return np.array(arr), tks_num
 
     def encode_queries(self, text):
+        # remove special tokens if they exist
+        for token in OllamaEmbed._special_tokens:
+            text = text.replace(token, "")
         res = self.client.embeddings(prompt=text, model=self.model_name, options={"use_mmap": True})
         try:
             return np.array(res["embedding"]), 128