returns the plain value (Any) if it exists, else return an empty Any
replaces some getUnpackedValueOrDefault calls in sw
where is was not clear if the unpacked value exsisted or was default

needed for removal of Any-to-Any template specialisations

Change-Id: I618da7a7174143f5edef48e47e7aa1b6a52845e1
Reviewed-on: https://gerrit.libreoffice.org/30114Tested-by: Jenkins <ci@libreoffice.org>
Reviewed-by: Stephan Bergmann <sbergman@redhat.com>