When the last parPart before a header was a bookmark, no span with an anchor was added for a bookmark in the header. But the function that adds header anchors to the anchor map, needs a span with an anchor. So this commit adds that span.
When the last parPart before a header was a bookmark, no span with an anchor was added for a bookmark in the header. But the function that adds header anchors to the anchor map, needs a span with an anchor. So this commit adds that span.