Fix: chat_completion answer data incorrect (#6041)

### What problem does this PR solve?

fix chat_completion answer data incorrect

### Type of change

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

Co-authored-by: renqi <renqi08266@fxomail.com>

api/apps/sdk/session.py

@@ -259,7 +259,7 @@ def chat_completion_openai_like(tenant_id, chat_id):
         # The choices field on the last chunk will always be an empty array [].
         def streamed_response_generator(chat_id, dia, msg):
             token_used = 0
-            should_split_index = 0
+            answer_cache = ""
             response = {
                 "id": f"chatcmpl-{chat_id}",
                 "choices": [
@@ -285,13 +285,9 @@ def chat_completion_openai_like(tenant_id, chat_id):
             try:
                 for ans in chat(dia, msg, True):
                     answer = ans["answer"]
-                    incremental = answer[should_split_index:]
+                    incremental = answer.replace(answer_cache, "", 1)
+                    answer_cache = answer.rstrip("</think>")
                     token_used += len(incremental)
-                    if incremental.endswith("</think>"):
-                        response_data_len = len(incremental.rstrip("</think>"))
-                    else:
-                        response_data_len = len(incremental)
-                    should_split_index += response_data_len
                     response["choices"][0]["delta"]["content"] = incremental
                     yield f"data:{json.dumps(response, ensure_ascii=False)}\n\n"
             except Exception as e: