The result of searching on a o2m field for a missing ID was
the whole set of records which do not have any lines in the
o2m fields. This is definitely not the desired behavior,
and could lead to disatrous performance, because the
returned set could be extremely large.

One example of such behavior is for recomputing fields
in the env cache in 8.0+. When a o2m line gets deleted,
it triggers the recompute of any dependent fields.

In order to locate the records to recompute, the ORM
searches for the 'parent' records in the comodel table.
When this operation is done by 2 users concurrently
the o2m line may not exist anymore, and the bug
is triggered: dependent fields are recomputed on a possibly
very large set of records that did not need any recompute!