[cff] 32bit integer overflow run-time errors 1/2 (#46149). This commit handles the old engine. * src/cff/cffgload.c: Include FT_INTERNAL_CALC_H. (cff_decoder_parse_charstrings): Use OVERFLOW_ADD_LONG and OVERFLOW_SUB_LONG where needed. * src/cff/cffparse.c: Include FT_INTERNAL_CALC_H. (power_ten_limits): New static array. (do_fixed): Use it to prevent multiplication overflow. (cff_parser_run): Use OVERFLOW_ADD_LONG.