fix reading a .doc that has frame anchored to the end of page (bnc#787942)

MSWord, unlike Writer, can anchor even to a page break (i.e. after the last
paragraph). When this document was read, what happended was:
- the last paragraph was read and the current position PaM was set to point
  after it
- frame was read and anchored to the PaM
- page break was read, making everything following be moved to the next page;
  including whatever ended up at the PaM position
Handle this by checking for this case and inserting an extra empty paragraph
before the break. This shouldn't affect layout of the page itself anyway,
since the break should leave room for it (and MSWord shows a page break
there if control characters are enabled, so there is room).

Change-Id: Ia2a13bf5cf1c959b5aa228254365019a00a22679
(cherry picked from commit 4a1888a97eab4ead2e0bec76cd1cba410a8e7e13)
Reviewed-on: https://gerrit.libreoffice.org/10952
Reviewed-by: Matúš Kukan <matus.kukan@collabora.com>
Tested-by: Matúš Kukan <matus.kukan@collabora.com>