Empty list items are merged with the previous line in CommonMark Markdown 1.2

Still reproducible on master after the 8.10.0 fixes, with a nested empty list item. For example, rendering the following xhtml/1.0 content to markdown/1.2:

<ul><li>a<ul><li></li></ul></li><li>c</li></ul>

gives

* a
    * 
* c

which is read back as a list item containing the text "a *" (the nested empty list is lost). Empty items at the first level of a list are now read back correctly.