Made more robust the function to evaluate a spline at a given distance.

src/g2_spline.cpp

@@ -865,8 +865,12 @@ void CG2Spline::generate(double &resolution,double n1,double n2, double n3, doub
 
 bool CG2Spline::evaluate(double length, TPoint& point)
 {
-  if (length < 0.0 || length > this->length[this->num_points-1])
+  if (length < -this->resolution || length > (this->length[this->num_points-1]+this->resolution))
     return false;
+  else if(length<0.0)
+    length=0.0;
+  else if(length>this->length[this->num_points-1])
+    length=this->length[this->num_points-1];
   point = this->evaluate_parameter(this->find_parameter(length));
   return true;
 }