perf: optimize WorkspaceService::getFile

[icewind1991]

📝 Summary

Optimize WorkspaceService::getFile by removing the separate check for nodeExists

🏁 Checklist

• [x] Code is properly formatted (npm run lint / npm run stylelint / composer run cs:check)
• [x] Sign-off message is added to all commits
• [x] Tests (unit, integration and/or end-to-end) passing and the changes are covered with tests
• [x] Documentation (README or documentation) has been updated or is not required