typioca crashes when cached cursor is out-of-bounds

When deleting local words' configuration, these cursors can get out-of-sync:
```
jq '.TestSettingCursors' ~/.cache/typioca/typioca.conf

{
  "TimerTimeCursor": 0,
  "TimerWordlistCursor": 0,
  "WordCountCursor": 0,
  "WordCountWordlistCursor": 0,
  "SentenceCountCursor": 0,
  "SentenceCountWordlistCursor": 0
}
```

Make sure we fallback to 0 if any of these are out-of-bounds.