[FIX] web: Basic model X2Many commands don't handled correctly

Steps to reproduce:

1. Go to the Accounting / Invoicing apps
2. Open Taxes (Configuration -> Accounting / Invoicing -> Taxes)
3. Try to create a new tax and the client crash.

It occurs because the `_processX2ManyCommands()` method doesn't handle
correctly a missing `fieldInfo` on some X2Many tags.

On mobile, when calling `load_views` the kanban view is used by default.
But if the kanban isn't defined, a default kanban view with only the id
of the model is used.

In the case of the taxes form, the `default_get` retrieved for this
form refers to a Many2Many (`tag_ids`) inside a One2Many. But this field
isn't present inside the loaded kanban view, so when we process the
command defined by the `default_get`, the `field_view` item doesn't
exist (because the default kanban loaded only contains the id of the
field).

Now instead of using an undefined `fieldInfo`, we fall back to an empty
object on the missing field to avoid the crash.

closes odoo/odoo#40612

X-original-commit: 47a306a31ac6d3c9e68e83b77a80426d5c6ceb05
Signed-off-by: res-odoo <res-odoo@users.noreply.github.com>