Rolled-up into footnotes require entry to have a body

[fluffy-critter]

Expected Behavior

{{entry.more}} should always render the entry's footnotes if there are any to render, even if there's no more-text or no footnotes.

Current Behavior

If nothing triggers the markdown renderer's footnote section, they don't get rendered. Oops.

Possible Solution

Move the footnote buffer flush stuff outside of the markdown renderer.

Steps to Reproduce (for bugs)

Two test cases:

Title: Footnotes in intro, no more-text

This is text.[^fn]

[^fn]: This is a footnote.

Title: Footnotes in intro, more-text with no footnotes

This is text.[^fn]

[^fn]: This is a footnote.

.....

This is more-text.

Context