[FIX] base_import: unscoped self can bear side effects

[blaggacao]

Access to an unscoped self (global context) can bear side effects.
This does not happen in standard Odoo, however in one instance, I found
a leaked self in the global context which obviously did not conform to
what is expected to be accessed here. self beeing volatile it is probably
an utterly bad idea to fetch it from the global context.

This PR access the windows invariant keyword instead.

Description of the issue/feature this PR addresses:

• Global self beard side effects in custom deployment
• As a consequence, the import wizard did not work

Current behavior before PR:

• Global self is accessed (without guarantees about it's shape)

Desired behavior after PR is merged:

• Global self is not accessed
• A more invariant window is accessed instead (maybe there is still a more suitable variable, but window does the trick)

--
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@xoe-labs

[C3POdoo]

Dear @blaggacao,

Thank you for your contribution but the version 12.0 is no longer supported.
We only support the last 3 stable versions so no longer accepts patches into this branch.

We apology if we could not look at your request in time.
If the contribution still makes sense for the upper version, please let us know and do not hesitate to recreate one for the recent versions. We will try to check it as soon as possible.

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