Redo produces an invalid state when undoing a break of an entity_reference

[michael]

Reproduce:

• In test article break entity reference (entity_reference_1)
• Undo that change and watch console

What happens:

• the undo reconstructs the previous state of the doc but somehow the writer-state points to the auto-created entityReferenceId that was valid before the undo.

[michael]

fixed.