fix: array access error when token.map is null, fix #3123

tests/lib/snapshots/markdown-test.js.md

@@ -4,6 +4,21 @@ The actual snapshot is saved in `markdown-test.js.snap`.
 
 Generated by [AVA](https://ava.li).
 
+## Markdown.render() should render footnote correctly
+
+> Snapshot 1
+
+    `<p data-line="1"><sup class="footnote-ref"><a href="#fn1" id="fnref1">[1]</a></sup><br />␊
+    hello-world: <a href="https://github.com/BoostIO/Boostnote/">https://github.com/BoostIO/Boostnote/</a></p>␊
+    <hr class="footnotes-sep" />␊
+    <section class="footnotes">␊
+    <ol class="footnotes-list">␊
+    <li id="fn1" class="footnote-item"><p>hello-world <a href="#fnref1" class="footnote-backref">↩︎</a></p>␊
+    </li>␊
+    </ol>␊
+    </section>␊
+    `
+
 ## Markdown.render() should render line breaks correctly
 
 > Snapshot 1