footnotes: Fix multiple paragraphs separated by blank lines

[robinst]

Fixes #388

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 94.82%. Comparing base (33737b7) to head (3111fed).
⚠️ Report is 2 commits behind head on main.

Additional details and impacted files

@@             Coverage Diff              @@
##               main     #389      +/-   ##
============================================
+ Coverage     94.79%   94.82%   +0.02%     
- Complexity      252      326      +74     
============================================
  Files           138      146       +8     
  Lines          4493     4789     +296     
  Branches        649      687      +38     
============================================
+ Hits           4259     4541     +282     
- Misses          129      134       +5     
- Partials        105      114       +9     

Files with missing lines	Coverage Δ
...rk/ext/footnotes/internal/FootnoteBlockParser.java	91.66% <100.00%> (ø)
...otnotes/internal/FootnoteMarkdownNodeRenderer.java	97.05% <ø> (ø)

... and 6 files with indirect coverage changes

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