Ensure ego observation road, lane, lane index fields are filled.

[Gamenot]

This addresses an issue where there are values in the ego observation that are not optional but return None.

[Adaickalavan]

While running a Waymo scenario, the following error popped up. Error message is truncated for brevity.

  File "/home/adai/workspace/SMARTS/competition/evaluation/.venv/lib/python3.8/site-packages/smarts/env/wrappers/format_obs.py", line 291, in observation
    val = func(getattr(agent_obs, self._stdob_to_ob[stdob]))
  File "/home/adai/workspace/SMARTS/competition/evaluation/.venv/lib/python3.8/site-packages/smarts/env/wrappers/format_obs.py", line 568, in _std_neighbors
    lane_index = np.array(lane_index, dtype=np.int8)
TypeError: int() argument must be a string, a bytes-like object or a number, not 'NoneType'
Exception ignored in: <function SMARTS.__del__ at 0x7f960ffb7c10>

The VehicleObservation.lane_index in obs.neighborhood_vehicle_states appears to be None. We have to make the same fix to the neighbours, as was made to the ego, to ensure neighbour vehicles don't have a lane_index=None.