Fix incorrect pixel offset in updatePixels()

[Forchapeatl]

Resolves #7139

Changes:

Screenshots of the change:

Before:

After :

PR Checklist

• npm run lint passes
• Inline documentation is included / updated
• Unit tests are included / updated

example usage

function setup() {
  createCanvas(400, 400);
}

function draw() {
  background(220);

  set(0, 0, [255, 0, 0, 255]); // red pixel at (0, 0)
  set(2, 2, [0, 0, 255, 255]); // blue pixel at (2, 2)
  updatePixels(2, 2, 1, 1);    // FIX : pixel at  (2, 2) is blue as expected
}

[Qianqianye]

Thanks @Forchapeatl!
@all-contributors please add @Forchapeatl for code

[allcontributors]

@Qianqianye

I've put up a pull request to add @Forchapeatl! 🎉