Regression from 13482889 (mismerge, I
guess), when header was enabled, actually empty footer was exported,
even in case footer was disabled.

(cherry picked from commit 4144cd5a)

Conflicts:
	sw/qa/extras/ww8export/ww8export.cxx

Change-Id: Ied55dc2a9f0faef87689c07935a47db384d37e1a
Reviewed-on: https://gerrit.libreoffice.org/3797Reviewed-by: Bosdonnat Cedric <cedric.bosdonnat@free.fr>
Tested-by: Bosdonnat Cedric <cedric.bosdonnat@free.fr>