[cff] Fix handling of `roll' op in old engine. Reported as https://bugs.chromium.org/p/oss-fuzz/issues/detail?id=10080 * src/psaux/cffdecode.c (cff_decoder_parse_charstrings) <cff_op_roll> [CFF_CONFIG_OPTION_OLD_ENGINE]: Use modulo for loop count, as documented in the specification.