Consider the following situation: a form view with a one2many which
contains sub x2many fields (for example a m2m_tags). Suppose that the
one2many has more than 40 records. Before this commit, trying to delete
one of these records caused a crash.
The reason is that when we delete a record, we need to reload the
missing records in the one2many field. We actually do that with a
_readUngroupedList. However, the _readUngroupedList method did not
process x2many fields, so the information stored in the datapoints was
'raw', and the rest of the web client expected it to be a datapoint.
To reproduce the issue in the testing environment, i had to use
onchanges and a readonly attrs, to reach a situation where a crash could
occur. This shows that, while the issue is critical, it was not totally
trivial to be impacted by it.