Refactor ManageStockCondition.php

[lbajsarowicz]

Description (*)

I found that ManageStockCondition.php uses == for if() conditions, although the Interfaces provided : bool for is... methods. I replaced them, but then realised that } else { is really crappy there, so I also replaced the mechanics to quick return conditions.

Fixed Issues (if relevant)

N/A

Manual testing scenarios (*)

N/A

Questions or comments

N/A

Contribution checklist (*)

• Pull request has a meaningful description of its purpose
• All commits are accompanied by meaningful commit messages
• All new or changed code is covered with unit/integration tests (if applicable)
• All automated tests passed successfully (all builds are green)

[lbajsarowicz]

Checks are failing because of the date used in Functional and Integration tests. Fixed already in magento/magento2#26225