Tocbot may break the post.min.js

[NichtsHsu]

NOTE: Before you start, the following should be completed.

• Read tutorial to understand the usage and the correct effect of functional design.
• Make sure no similar issue(including closed ones) exists.
• Make sure the bug is found in the latest code of the master branch.

Describe the bug

If a post do not have headers, tocbot.min.js will not be loaded becuase of:

jekyll-theme-chirpy/_includes/toc.html

Lines 8 to 16 in 6fec411

	{% if enable_toc %}
	<div id="toc-wrapper" class="pl-0 pr-4 mb-5">
	<div class="panel-heading pl-3 pt-2 mb-2">{{- site.data.locales[site.lang].panel.toc -}}</div>
	<nav id="toc"></nav>
	</div>
	<!-- toc.js will be loaded at medium priority -->
	<script src="{{ site.data.assets[origin].toc.js | relative_url }}"></script>
	{% endif %}

But toc.js in post.min.js still executes and then cause a tocbot is not defined error, which will break post.min.js. I've added some custom scripts at the end of post.js, and they can't be executed in a post without headers for the reason mentioned above.

To Reproduce

Steps to reproduce the behavior:

1. Create a post without any headers.
2. Check console messages.

Expected behavior

Logs/Screenshots

Environment

Command	Version
ruby -v	3.0.2p107
gem -v	3.3.5
bundle -v	2.3.13
bundle exec jekyll -v	4.3.2
bundle info jekyll-theme-chirpy	5.6.0

Additional context