fix: Ensure fallback works for LDCs

[DafyddLlyr]

Before

• An LDC is received (e.g. lds.listedBuildingWorks)
• It does not have a value found in ldcDescriptionFns
• The .join("; ") operations converts the empty array to the falsy ""
• The fallback condition "Not provided" is reached - despite there being a valid proposal.description ❌

After

• An LDC is received (e.g. lds.listedBuildingWorks)
• It does not have a value found in ldcDescriptionFns
• Fallback to proposal.description if possible, otherwise just "Not provided" ✅

There might well be a content solution alongside this, for example have a LDC LBW specific description field, but having this fallback in place should prevent future issues here.