[16.0] sale_margin_security: error creating invoices

[dreispt]

Module

sale_margin_security

Describe the bug

A user without the "Show Sale Margin" access group can't create invoices.

To Reproduce

Create an Invoice from a Sale Order, found in 16.0.

Expected behavior
A user without the "Show Sale Margin" access group can't see the margin fields, but should still be able to create Invoices as usual.