adding is_empty flag for prevent panic

[kyoto7250]

close #142

• This PR adds offset is_empty flag for preventing panic in a filter.
  • this flag looks at the length of the list rather than the offset, so I'll rename it (PS. 2022/04/15)

This bug is caused by a moving ownership in a closure.

https://github.com/TaKO8Ki/gobang/blob/b13e4bb255ea533db16240e1cb5138fca4241264/src/components/completion.rs#L77-L83

I think if ListState is hidden and input is down or up arrow, then the ListState is not updated, and try to acccess to already moved variable again.

However, I didn't see a problem with the current closure implementation, so I responded by adding a flag to not call the closure if ListState is not displayed.

Thank you in advance.

changelog: Adding is_empty flag for prevent panic.