Car 4D Example Issue: cbf < 0 happens even when velocity is always positive.

[goldenhazard]

commit_id : 63053cd

Please run demos/run_cbf_car4D to reproduce this issue.

After an adaptation of the u_min to saturate to zero, when v <= v_min - dt*u_min, it prevented the velocity from going under zero, but infeasibility happens, which makes the CBF constraint violated.