Update chat_template.jinja

Add case where generation prompt is not specified.

chat_template.jinja

@@ -83,4 +83,6 @@
 {%- endfor %}
 {%- if add_generation_prompt %}
     {{- '<|im_start|>assistant\n<think>\n\n</think>\n\n<reasoning>\n'}}
+{%- else %}
+    {{- '<|im_start|>assistant\n<think>\n\n</think>\n\n'}}
 {%- endif %}