Fix Cartesian interpolation with multiple waypoints

continue from latest RobotState

moveit_core/robot_state/src/cartesian_interpolator.cpp

@@ -298,6 +298,7 @@ CartesianInterpolator::Percentage CartesianInterpolator::computeCartesianPath(
       percentage_solved += wp_percentage_solved / static_cast<double>(waypoints.size());
       break;
     }
+    start_state = traj.back().get();
   }
 
   return percentage_solved;