[FIX] crm: date_closed when writting without probability value

If `probability` is not being written,
`vals.get('probability')` is `None`
`None` < 100 is `True`

While it should not remove the `date_closed` value
when the probability field is not being rewritten
on the lead, but something else is.

opw-677273

addons/crm/crm_lead.py

@@ -906,7 +906,7 @@ class crm_lead(format_address, osv.osv):
             vals.update(onchange_stage_values)
         if vals.get('probability') >= 100 or not vals.get('active', True):
             vals['date_closed'] = fields.datetime.now()
-        elif vals.get('probability') < 100:
+        elif 'probability' in vals and vals['probability'] < 100:
             vals['date_closed'] = False
         return super(crm_lead, self).write(cr, uid, ids, vals, context=context)