Now the `OnEventView.on_pre_event_inner()` calls return
`Some(EventResult::Consumed(Some(Callback)))` instead of
`Some(EventResult::Consumed(None))`.
This follows the guidelines from documentation of methods returning a
`Callback`, which say that it should be ran on the `Cursive`.
While in this example this doesn't make a difference, the previous
version created confusion for new users who might not realize you can
pass the `Callback`s to the `Cursive` this way.
