utils/oscap-cvrf: Fix the leak of import_source, add NULL check
utils/oscap-cvrf: Fix the leak of import_source, add NULL check

redhatrises/openscap,OpenSCAP/openscap,OpenSCAP/openscap,redhatrises/openscap,OpenSCAP/openscap,redhatrises/openscap,redhatrises/openscap,OpenSCAP/openscap,redhatrises/openscap,redhatrises/openscap,OpenSCAP/openscap,OpenSCAP/openscap