When a header/footer substream is parsed, a ParagraphGroup is started,
but not ended; so the properties of the last paragraph in the
header/footer are applied to a paragraph in the body.

The obvious fix to add a call to endParagraphGroup() at the end of w:p
element breaks table cells.  So add a call to endParagraphGroup() at
the end of the "hdr"/"ftr" element.

(The problem in the bugdoc became much more visible with commit
ca555c59, but was there before)

Change-Id: Ib054f1882793049b39424c1076ba5d4b319cd027