fix: [signing] fail gracefully if pgp not configured on event index
fix: [signing] fail gracefully if pgp not configured on event index

- return the index, but set fingerprint as null rather than throwing an exception

MISP/MISP,SteveClement/MISP,SteveClement/MISP,MISP/MISP,SteveClement/MISP,SteveClement/MISP,MISP/MISP,MISP/MISP,SteveClement/MISP,MISP/MISP