[BUG] Footnote on Slide prohibts Speaker Notes on same Slide

## Markdown source
On hackmd.io: https://hackmd.io/B1iWgVmnV?both
Slides on hackmd.io: https://hackmd.io/p/B1iWgVmnV
```markdown
# 1234

---

## 1 [^one]

[^one]: https://one.com

---

## 2

Note:
- two

---

## 3[^three]

[^three]: https://three.com

Note:
- three

---

## 4[^four]

Note:
- four

[^four]: https://four.com
```

## Expected Behavior
When clicking `s` in the presentation and going to slide 3, the list text `- three` should be visible in the speaker notes.

## Actual Behavior
The speaker notes of slide 3 are empty.

## Possible Cause
The footnote on the slide seems to be cause the absent speaker note.