Regression from:
83d51e5e

Partly revert the commit causes this regression.
I checked the related bugs (tdf#78590,tdf#80748)
intended to be fixed by this commit and reverting
this part does not bring back the corruption.
I guess something changed in frames' and text boxes'
import in the meantime, because this MergeMarks::IGNORE
is useless now.

Change-Id: If17776e8628561961c7ce2a2994e3fc609f75639
Reviewed-on: https://gerrit.libreoffice.org/30351Reviewed-by: Tamás Zolnai <tamas.zolnai@collabora.com>
Tested-by: Tamás Zolnai <tamas.zolnai@collabora.com>