fix: [stix1 import] Avoiding AttributeError exceptions when the STIX packages have no header
fix: [stix1 import] Avoiding AttributeError exceptions when the STIX packages have no header

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