fix: panic on key up/down

[dzfrias]

Fixes #15

[EdJoPaTo]

While this fixes the issue by preventing it in the first place it's not solving the underlying issue: using slice[index] which can panic. Personally I would go for fixing it by moving over to slice.get(index) which returns an Option instead. Then this option can be handled cleanly. This sounds cleaner to me.

-let new_identifier = visible[new_index].identifier.clone();
+let new_identifier = visible
+    .get(new_index)
+    .map(|o| o.identifier.clone())
+    .unwrap_or_default();

What do you think?

[dzfrias]

That sounds good; I can replace it with that!

[EdJoPaTo]

Thank you for your time proving the PR and your report about this issue!