(Bug 52751): Serialize p-wrapped list items correctly

* Commit c0de1d58 passed in a wrong param into a method which
  caused the regression for the example in the bug report

  "<ul><li><p>a</p></li></ul>" serializes to "*\na" instead of "* a"

* Fixed + added new parser test.

Change-Id: I30bf07bc7dabbb192bb066d8c7cf18b76e28d408
Merge "(Bug 52751): Serialize p-wrapped list items correctly"