List parsing affected by number of blank lines at end

[jgm]

See jgm/pandoc#6589

% commonmark
- a
  - b
  - c
^D
<ul>
<li>a
<ul>
<li>b
</li>
<li>c
</li>
</ul>
</li>
</ul>

% commonmark
- a
  - b
  - c



^D
<ul>
<li>a
<ul>
<li>
<p>b</p>
</li>
<li>
<p>c</p>
</li>
</ul>
</li>
</ul>

[jgm]

Here is the culprit:

         let blanksAtEnd = case blanks of
                                     (l:_) -> l >= curline - 1
                                     _     -> False
            let blanksInside = case length blanks of
                                  n | n > 1     -> True
                                    | n == 1    -> not blanksAtEnd
                                    | otherwise -> False

This assumes at most one blank line at the end.

[jgm]

We were doing removeConsecutive which will remove runs of 2+ blank lines for this test.
However, the test for a blank at end fails after this. Should be easy to fix.