[FIX] calendar: in multicompany user cannot access own calendar

Let's consider user1 and user2 allowed to access company1 and company2
In multicompany with shared partners unchecked in general settings,
if one of two users sharing the same event tried to access the event
when they are not in the same current company at this moment, an access error
was raised.

opw:1817475

addons/calendar/models/calendar.py

@@ -841,7 +841,7 @@ class Meeting(models.Model):
 
     @api.multi
     def _compute_color_partner(self):
-        for meeting in self:
+        for meeting in self.sudo():
             meeting.color_partner_id = meeting.user_id.partner_id.id
 
     @api.constrains('start_datetime', 'stop_datetime', 'start_date', 'stop_date')