message: improve concat to avoid deopt with empty
diff: @@ -118,6 +118,12 @@ export function single<A>(a: A): Chunk<A> {
  }
  export function concat_<A>(x: Chunk<A>, y: Chunk<A>): Chunk<A> {
  + if (x === empty) {
  + return y
  + }
  + if (y === empty) {
  + return x
  + }
  if (Buffer && Buffer.isBuffer(x) && Buffer.isBuffer(y)) {
  return buffer(Buffer.concat([x, y]))
  }
  