Fix post-blank for headlines containing only whitespace.

src/parser/headline.rs

@@ -67,6 +67,7 @@ fn _heading<'b, 'g, 'r, 's>(
     let section_matcher = bind_context!(section, context);
     let heading_matcher = bind_context!(heading(pre_headline.star_count), context);
     let (contents_begin, _) = opt(many0(blank_line))(remaining)?;
+    let maybe_post_blank = get_consumed(remaining, contents_begin);
     let (remaining, maybe_section) =
         opt(map(section_matcher, DocumentElement::Section))(remaining)?;
     let (remaining, _ws) = opt(tuple((start_of_line, many0(blank_line))))(remaining)?;
@@ -83,7 +84,8 @@ fn _heading<'b, 'g, 'r, 's>(
         }
         children.insert(0, section);
     }
-    let remaining = if children.is_empty() {
+    let has_children = !children.is_empty();
+    let remaining = if !has_children {
         // Support empty headings
         let (remain, _ws) = many0(blank_line)(remaining)?;
         remain
@@ -119,6 +121,11 @@ fn _heading<'b, 'g, 'r, 's>(
             } else {
                 None
             },
+            post_blank: if has_children {
+                None
+            } else {
+                Some(Into::<&str>::into(maybe_post_blank))
+            },
         },
     ))
 }