Gradient fill calculates x2 coordinate incorrectly within imagefilledrectangle()

To reproduce behavior, set coordinates of gradient in color.inc to something like:

  // Coordinates of gradient (x, y, width, height)
  'gradient' => array(1120, 187, 49, 24),

Notice that instead of starting at 1120, it starts at 49. This is because the third coordinate is not actually the width; it is the x2 coordinate (x2 = x + width).

I have provided a patch to resolve this issue inside the color.module. (see attached)