Incorrect formula to calculate the linnear position.

[git-tomas]

Imagine/src/Utils/Matrix.php

Lines 169 to 176 in c10ea7f

	protected function calculatePosition($x, $y)
	{
	if ($x < 0 || $y < 0 || $this->width <= $x || $this->height <= $y) {
	throw new OutOfBoundsException(sprintf('There is no position (%s, %s) in this matrix', $x, $y));
	}
	return $y * $this->height + $x;
	}

The formula must be return $y * $this->width + $x;

[ausi]

I think you are right. Would you mind creating a pull request (including a unit test) that fixes this issue?