Fix crash when selecting static models without links by adding empty check

[XINJIANGMO]

🦟 Bug fix

Fixes #3077

Summary

The crash is triggered by loading a static model without any link, then opening the ApplyForceTorque plugin and toggling the selected object from normal to static The plugin attempts to access an empty linkNameList , leading to an illegal memory access and segmentation fault.

Checklist

• Signed all commits for DCO
• Added tests
• Updated documentation (as needed)
• Updated migration guide (as needed)
• Consider updating Python bindings (if the library has them)
• codecheck passed (See contributing)
• All tests passed (See test coverage)
• While waiting for a review on your PR, please help review another open pull request to support the maintainers

[arjo129]

Thanks for the intense fuzz testing and bug fixing @XINJIANGMO !!

[azeey]

@caguero We need a prerelease of gz-transport to fix Ubuntu Noble CI on github actions.