[no-ticket] fix: don't always populate OR_GrowthRateFloor variable

[Lkruitwagen]

Description

• only populate OR_GrowthRateFloor variable if the user has specified these constraints (otherwise the dual values are 0.)

Checklist

• Dependencies install correctly in a clean environment and code executes;
• Test coverage extended; created tests fail without the change (if possible);
• All tests passing;
• Commits follow a type convention (e.g. https://gist.github.com/brianclements/841ea7bffdb01346392c#type);
• Extended the README, documentation and/or docstrings, if necessary;