Bug: Use of `assert` prevents code from being executed when optimization is turned on

[foobarzap]

In utilities.swift:

  internal mutating func skip(_ n: Int) {
        guard n < count else {
            self = Data()
            return
        }
        for _ in 0..<n {
            // -> popFirst() doesn't get executed if optimization is turned on!
            assert(popFirst() != nil)
        }
    }

Possible fix:

  internal mutating func skip(_ n: Int) {
        guard n < count else {
            self = Data()
            return
        }
        for _ in 0..<n {           
            let check = popFirst()
            assert(check != nil)
        }
    }