fix: `clear_thinking` inserts spurious `</think>` tag when reasoning_content is empty

chat_template.jinja

@@ -49,11 +49,14 @@ For each function call, output the function name and arguments within the follow
         {%- set content = content.split('</think>')[-1].lstrip('\n') %}
     {%- endif %}
 {%- endif %}
-{%- if ((clear_thinking is defined and not clear_thinking) or loop.index0 > ns.last_user_index) and reasoning_content -%}
-{{ '<think>' + reasoning_content.strip() +  '</think>'}}
-{%- else -%}
-{{ '</think>' }}
+{#- FIXED: clear_thinking=true means clear thinking content, no thinking tags at all -#}
+{%- if clear_thinking is not defined or not clear_thinking -%}
+    {#- clear_thinking=false or undefined: keep thinking content -#}
+    {%- if reasoning_content -%}
+{{ '<think>' + reasoning_content.strip() + '</think>' }}
+    {%- endif -%}
 {%- endif -%}
+{#- clear_thinking=true: only output content, no thinking tags -#}
 {%- if content.strip() -%}
 {{ content.strip() }}
 {%- endif -%}
@@ -83,4 +86,5 @@ For each function call, output the function name and arguments within the follow
 {%- endfor -%}
 {%- if add_generation_prompt -%}
     <|assistant|>{{- '</think>' if (enable_thinking is defined and not enable_thinking) else '<think>' -}}
-{%- endif -%}
+
+{%- endif -%}