fix(lanelet2_map_validator): fixed issue that invalid prerequisites are not reflected to the results

[TaikiYamada4]

Description

This PR fixes the issue that the validation results (lanelet2_validation_results.json) don't reflect the prerequisite failure.
The content in prerequisite_issues should be written in the JSON objects, but the process between L319 to L355 (in validation.cpp) is skipped only for prerequisite_issues.

Related links

None

Tests performed

• Checked that colcon test has passed.
• Checked that issues with a message "Prerequisites didn't pass." appear in lanelet2_map_validation_results.json when a incomplete lanelet2 map is given.

Notes for reviewers

Interface changes

Effects on system behavior

Prerequisites failure will appear in the results as expected.

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