BoundingBox calculation fails in certain cases about bonsai HOT 3 CLOSED

// Source: http://blog.hackers-cafe.net/2009/06/how-to-calculate-bezier-curves-bounding.html
// Original version: NISHIO Hirokazu
// Modifications: Timo
function getBoundsOfCurve (x0, y0, x1, y1, x2, y2, x3, y3)
{
  var tvalues = [], bounds = [new Array(6), new Array(6)],
      a,b,c,t,t1,t2,b2ac,sqrtb2ac;
  for (var i = 0; i < 2; ++i)
  {
    if (i==0)
    {
      b = 6 * x0 - 12 * x1 + 6 * x2;
      a = -3 * x0 + 9 * x1 - 9 * x2 + 3 * x3;
      c = 3 * x1 - 3 * x0;
    }
    else
    {
      b = 6 * y0 - 12 * y1 + 6 * y2;
      a = -3 * y0 + 9 * y1 - 9 * y2 + 3 * y3;
      c = 3 * y1 - 3 * y0;
    }
    if (abs(a) < 1e-12)
    {
      if (abs(b) < 1e-12) continue;
      t = -c / b;
      if (0 < t && t < 1) tvalues.push(t);
      continue;
    }
    b2ac = b*b - 4 * c * a;
    sqrtb2ac = sqrt(b2ac);
    if (b2ac < 0) continue;
    t1 = (-b + sqrtb2ac) / (2 * a);
    if (0 < t1 && t1 < 1) tvalues.push(t1);
    t2 = (-b - sqrtb2ac) / (2 * a);
    if (0 < t2 && t2 < 1) tvalues.push(t2);
  }

  var j = tvalues.length, jlen = j, mt;
  while(j--)
  {
    t = tvalues[j]; 
    mt = 1-t;
    bounds[0][j] = (mt*mt*mt*x0) + (3*mt*mt*t*x1) + (3*mt*t*t*x2) + (t*t*t*x3);
    bounds[1][j] = (mt*mt*mt*y0) + (3*mt*mt*t*y1) + (3*mt*t*t*y2) + (t*t*t*y3);
  }

  //tvalues[jlen] = 0;
  //tvalues[jlen+1] = 1;
  bounds[0][jlen] = x0;
  bounds[1][jlen] = y0;
  bounds[0][jlen+1] = x3;
  bounds[1][jlen+1] = y3;
  bounds[0].length = bounds[1].length = jlen+2;

  return {
    left: min.apply(null, bounds[0]),
    top: min.apply(null, bounds[1]),
    right: max.apply(null, bounds[0]),
    bottom: max.apply(null, bounds[1])
  };
};