possible bug

If i add full 1-byte range from 0x00 to 0xff. TrieChar 255 appears int the results of trie_state_walkable_chars() or trie_enumerate(). 

1byte.abm
```
[0x0,0xff]
```

```
trietool 1byte add 12
trietool 1byte add 122
trietool 1byte list
12ÿ	-1
122	-1
ru@ru-mi:/usr/local/libdatrie/bin# 
```

