... to avoid "corrupted" warning from Excel.
In case of string fields, Excel expects the item list to be present,
and containsXXX attributes of sharedItems to be absent, otherwise
it shows a warning about file corruption.
For numeric fields, it doesn't expect item list, othervise it also
warns about file corruption.

Change-Id: I5ded5b836587bed3177eb0a6b6c418e459e6be8b
Reviewed-on: https://gerrit.libreoffice.org/39114Tested-by: Jenkins <ci@libreoffice.org>
Reviewed-by: Mike Kaganski <mike.kaganski@collabora.com>