[FIX] core: unexpected MissingError when prefetching record

This is a rare case where method _read() raises a MissingError instead
of just ignoring it.

The issue is triggered by several conditions on a model M:
 - at least one ir.rule on M with a domain using a column field on M;
 - one deleted record Y which is in the prefetch set of a record X;
 - one reads a non-column field on record X.

Fix method _read() to manage that case.  It adds an extra call to
exists() in that case, but adds no overhead in the general case.

closes odoo/odoo#107883

Signed-off-by: Rémy Voet <ryv@odoo.com>