Support list items with empty first line

also dismiss implementing ordered list bullet overrides for now, e.g.
1. [@10] foo

add it once someone needs it - for now it seems like needless complexity

org/testdata/lists.org

@@ -1,10 +1,17 @@
 - [ ] unordered list item 1
+-
+
+  list item with empty first and second line \\
+  normally an empty line breaks the list item - but we make an exception for the first line and don't count it towards that limit
 - unordered list item 2 - with ~inline~ /markup/
   1. [-] ordered sublist item 1
      a) [X] ordered sublist item 1
      b) [ ] ordered sublist item 2
      c) [X] ordered sublist item 3
   2. ordered sublist item 2
+  3.
+
+     list item with empty first and second line - see above
 - [X] unordered list item 3 - and a [[https://example.com][link]]
   and some lines of text
   1. and another subitem