[16.0][FW][FIX] operating_unit: default operating unit more multi-company friendly

[aleuffre]

FW of #642

This PR fixes an issue with the method operating_unit_default_get where it would return an operating unit even for a company that was not active, which would cause all sorts of issues

Steps to reproduce on runboat, taking as example purchase_operating_unit:

• User has a default ou belonging to Company 1
• Switch to Company 2 (make sure Company 1 is not active at all)
• Try to create a Purchase Order

The issue arises because the operating_unit field is pre-compiled on the PO with an Operating Unit whose company is inactive, and the onchanges cannot find or access related data.

[AaronHForgeFlow]

/ocabot merge patch

[OCA-git-bot]

Hey, thanks for contributing! Proceeding to merge this for you. Prepared branch 16.0-ocabot-merge-pr-644-by-AaronHForgeFlow-bump-patch, awaiting test results.

[OCA-git-bot]

Congratulations, your PR was merged at 093c0729a78c3a76b1036d457e82d2be82c34faf. Thanks a lot for contributing to OCA. ❤️