contact merge issue with abstract reference fields

[CGenie]

Impacted versions: 9, 10, 11

Steps to reproduce:
Create an abstract model with a reference field, for example one that was suggested by the Connector module:
https://github.com/OCA/connector-prestashop/blob/9.0/connector_prestashop/models/binding/common.py#L51-L56

Current behavior:
When merging contacts, an error is thrown that the above abstract model has no database relation (table).

Expected behavior:
Do not query that model at all since it's abstract.

In particular, add the following check:

if not Model._auto:
    continue

somewhere here:

• verison 11: https://github.com/odoo/odoo/blob/11.0/addons/crm/wizard/base_partner_merge.py#L208-L209
• version 10: https://github.com/odoo/odoo/blob/10.0/addons/crm/wizard/base_partner_merge.py#L245-L246
• version 9 (change Model in the above to proxy_model): https://github.com/odoo/odoo/blob/9.0/addons/crm/base_partner_merge.py#L255-L256

[C3POdoo]

Dear @CGenie,

Thank you for your report but we are closing it due to inactivity.
We apology if we could not look at your request in time.
If your report still makes sense, don't hesitate to reopen a new one. We will try to check it as soon as possible.

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