fsm_location.partner_id field in form view prevents creation when debug is active

[are-agilebg]

Hi,

I have found this strage behavior in the module fieldservice, which affects 15.0 and 16.0 branches (probably even 17.0 but I haven't checked).

Steps to reproduce on Runboat:

• activate the debug mode (put the debug=1 parameter in the URL, use the browser extension, whatever)
• go to 'Field Service > Master Data > Locations'
• click on 'Create'
• fill 'Name', 'Related Owner' and 'Billed Customer'
• click on 'Save'

An error will prevent saving the record showing: 'Invalid fields: Related Partner'.

The problem is that the field is readonly=True, required=True and False since it hasn't been created.

This is particularly nasty in instances that uses base_technical_features to always show technical fields even to users without administration privileges.

The same problem cannot exist in version 14.0 which declares the field required=False in the view.

I'm not opening a PR now since I'm afraid I could be missing something: let me know If I'm right at seeing it as a bug or not.