Avoid unwrapping in libterm

[frewsxcv]

Instead of this:

                        if !stack.is_empty() {
                            match stack.pop().unwrap() {
                                ...
                            }
                        } else {
                            ...
                        }

do:

                        match stack.pop() {
                            Some(..) => ...
                            None => ...
                        }

---

Similarly, instead of this:

                        if stack.len() > 1 {
                            match (stack.pop().unwrap(), stack.pop().unwrap()) {
                                (Number(y), Number(x)) => ...
                                _ => ...
                            }
                        } else {
                            ...
                        }

do:

                        match (stack.pop(), stack.pop()) {
                            (Some(Number(y)), Some(Number(x))) => ...
                            (Some(_), Some(_) => ...
                            _ => ...
                        }

There are multiple instances of these patterns in this file so make sure to clean up all of them

[SingingTree]

Gonna have a go at this one unless anyone has already grabbed it.

[Stebalien]

Or you could just re-import the current term crate (where I fixed this about a week ago)...

[untitaker]

This may be closed, I don't see any unnecessary unwraps in libterm anymore.