message: allow views of undefined columns
diff: @@ -364,7 +364,7 @@ function isIdentity(map: ArrayLike<number>, rowCount: number) {
  }
  function columnView<T>(c: Column<T>, map: ArrayLike<number>, checkIdentity: boolean): Column<T> {
  - if (!c.isDefined || c.rowCount === 0) return c;
  + if (c.rowCount === 0) return c;
  if (checkIdentity && isIdentity(map, c.rowCount)) return c;
  if (!!c.__array && typeof c.value(0) === typeof c.__array[0]) return arrayView(c, map);
  return viewFull(c, map);
  