[views/forms] Fix EntityFieldsForm.link_to when parent entity is being created When the parent entity is being created and the inlined form is displayed, the parent entity has no eid yet and `peid` is usually 'A'. So int() raises a ValueError. Closes #4627739.

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raise NotImplementedError("Cannot migrate such an old version. Use intermediate Cubiweb version (try 3.16.x)")