[FIX] base: clear cache before read access check

When reading binary content such as `image_128` on `res.users`,
`AccessError` should be raised when necessary.

Steps to reproduce:
  - Populate cache in superuser mode.
  - Access cached field with public user.
  - Read access is allowed but should not.

Concrete example:
  - Unpublish `demo` user.
  - Access `/slides` with `public` user.
  - The template data is generated as `sudo`.
  - The same data is then accessed as `public`.
  - AccessError should be raised when requesting
    `/profile/avatar/<int:user_id>` but is not.

Closes #43826

Signed-off-by: Christophe Simonis <chs@odoo.com>