fix default system prompt

chat_template.jinja

@@ -52,10 +52,11 @@
   <|im_system|>tool_declare<|im_middle|>{{ tools | tojson(separators=(',', ':')) }}<|im_end|>
 {%- endif -%}
 
-{%- for message in hist_msgs -%}
-  {%- if loop.first and messages[0]['role'] != 'system' -%}
+{%- if messages|length == 0 or messages[0]['role'] != 'system' -%}
   <|im_system|>system<|im_middle|>You are Kimi, an AI assistant created by Moonshot AI.<|im_end|>
-  {%- endif -%}
+{%- endif -%}
+  
+{%- for message in hist_msgs -%}
   {{set_roles(message)}}
   {%- if message['role'] == 'assistant' -%}
     <think></think>{{render_content(message)}}