Revert "no need to have duplicate m_nStorageType fields"
This reverts commit 9a9bb1f212.
Change-Id: Ia471d291ebb99aea47c798cf923d7571711de356
Reviewed-on: https://gerrit.libreoffice.org/c/core/+/197118
Tested-by: Jenkins
Reviewed-by: Noel Grandin <noel.grandin@collabora.co.uk>