Avoid "Jump" when scrolling for the first time

[moritzebeling]

After page load, the parallax offset is calculated.
But when you first start scrolling, parallax elements do a jump and then continue to move smoothly.

This means, that the first initial parallax position must be incorrect.

[moritzebeling]

As a first hack, I caused a redraw immediately after setting up all elements:

setTimeout(() => {
  context.onScroll();
}, 1);