Use optional bindings to limit forced unwrapping

[ayoy]

advent-swift/Sources/advent2019/day2.swift

Line 16 in c1bae58

if (noun != nil) { memory[1] = noun! }

A Swifty way to do this would be:

if let validNoun = noun {
    memory[1] = validNoun
}

or even:

if let noun = noun {
    memory[1] = noun // shadowing function parameter is fine in a one-line block
}