fix(autoware_behavior_path_lane_change_module): avoid empty current lanes

[KYabuuchi]

Description

Overview:

I have modified the lane change module so that it can utilize current_lanes even if target_lanes is empty.

Details:

When driving manually with Autoware activated, sometimes target_lanes would be empty, which would cause current_lanes to be empty as well.
If current_lanes is empty, an error occurs in the current_lanes.back() that is called afterwards.

Specifically, I encountered the error at utils::lane_change::calcMinimumLaneChangeLength(
route_handler, current_lanes.back(), *lane_change_parameters_, direction_);

Related links

Parent Issue:

• Nothing

Private Links:

• TIER IV internal ticket link
• TIER IV internal slack link

How was this PR tested?

I tested by logging simulator with the TIER IV private rosbag and verified that the planner is now stable and no longer aborts.

Notes for reviewers

Recently, this phenomenon has become more frequent, but the reason why target_lanes becomes empty during manual driving remains unclear.

Interface changes

Does not change.

Effects on system behavior

Does not change.

[sonarcloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarCloud

[shmpwk]

LGTM