When exporting ooo67907-1.doc we get ~SwIndexReg assert because there's
a frame anchored in a redline, and the SwPosition in the sw::Frame for
it is invalidated during SetRedlineMode because the node it points to is
deleted.  Add another horrible workaround to the redline trainwreck.

Change-Id: Ia9b2393c77f42502862daaa30fd54eb3b040a214
(cherry picked from commit ab706f85)
Reviewed-on: https://gerrit.libreoffice.org/17231Tested-by: Jenkins <ci@libreoffice.org>
Reviewed-by: Caolán McNamara <caolanm@redhat.com>
Tested-by: Caolán McNamara <caolanm@redhat.com>