Reset both sec and nanosec in time_from_start (backport #1709) (#1710)

Co-authored-by: Arnav Kapoor <[email protected]>

Author: mergify[bot]

joint_trajectory_controller/src/joint_trajectory_controller.cpp

@@ -193,7 +193,8 @@ controller_interface::return_type JointTrajectoryController::update(
   };
 
   // current state update
-  state_current_.time_from_start.set__sec(0);
+  state_current_.time_from_start.sec = 0;
+  state_current_.time_from_start.nanosec = 0;
   read_state_from_state_interfaces(state_current_);
 
   // currently carrying out a trajectory