[cff] Fix more value errors and improve tracing. * src/cff/cffparse.c (cff_parse_integer): Emit tracing message in case of error. (cff_parse_real): Handle and trace overflow, underflow, and bad data consistently. (do_fixed): New helper function, handling and tracing overflow. (cff_parse_fixed, cff_parse_fixed_scaled): Use `do_fixed'.