...which matches the original situation better, where ContentTypeId was
sal_uInt16, and so the default -1 for
/org.openoffice.Office/Writer/Navigator/RootType happened to match UNKNOWN being
USHRT_MAX.  Follow-up to 874cc6cb "Don't read
out-of-range ContentTypeId from configuration."

Change-Id: I6d136412982c3cfb06ddef3b6c1acd800d92ae05