[sfnt] Further generalize `sfnt_get_ps_name'; report invalid data. * src/sfnt/sfdriver.c (sfnt_ps_map): New array. (sfnt_is_postscript): New function. (char_type_func): New typedef. (get_win_string, get_apple_string): Add argument to specify character checking function. Add argument whether argument checking failures should be reported. Update callers. (search_name_id): Fix return value.