tdf115103: find data source if sDataSource/sCommand are empty
In several functions data source was only found if sDataSource and
sCommand corresponded to what was set in fields.
In imported DOC(X) files these aren't set.
Now use the data source even if field's sDataSource/sCommand are
empty (similarly to SwDBManager::IsDataSourceOpen(...)).
Change-Id: I9563cb56e700e7fd033100cb200f41f074669020
Reviewed-on: https://gerrit.libreoffice.org/48285
Tested-by: Jenkins <ci@libreoffice.org>
Reviewed-by: Aron Budea <aron.budea@collabora.com>