[FIX] sale: portal generates pdf for the chatter in a separate request

Steps to reproduce:
- install studio, website and sales
- go to sales > open studio > go to 'reports' > Quotation/Order
- add a field anywhere on the report with the field expression set to
"doc.signature" > save
- go to sles > create a quotation > send by email > send > go to the customer portal
- sign and send the quotation > go back to the edit mode > open the pdf attached
to the latest message in the chatter

Previous behavior:
the custom field added was not rendered properly,
the attachment is not available during the request and the generated
pdf shows the placeholder image instead

Current behavior:
the message posted in the chatter is generated in another request,
this makes the attachment available

opw-2260989

closes odoo/odoo#54955

X-original-commit: a15cbb0a7be666d3ad438f6470d29cda75c24027
Signed-off-by: Nicolas Lempereur (nle) <nle@odoo.com>
Signed-off-by: Nicolas Martinelli (nim) <nim@odoo.com>

addons/sale/controllers/portal.py

@@ -224,6 +224,7 @@ class CustomerPortal(CustomerPortal):
                 'signed_on': fields.Datetime.now(),
                 'signature': signature,
             })
+            request.env.cr.commit()
         except (TypeError, binascii.Error) as e:
             return {'error': _('Invalid signature data.')}