Nokogiri before 1.19.1 Unchecked Return Value canonicalize

Nokogiri versions before 1.19.1 fail to check the return value from xmlC14NExecute in the canonicalize method, returning an empty string on failure instead of raising an exception. Attackers can exploit this to bypass signature validation in downstream SAML libraries by providing invalid canonicalized XML that is incorrectly accepted as valid.