[FIX] calendar: do not create events past year 9999

datetime.date(year, month, day).weekday() is undefined for year > 9999.
When creating a google recurrent event that is set to never end,
Odoo tries to create 100 individual events.
If in Google calendar the user sets a recurring event to a custom interval,
of say a century, then the hundredth event is in 100x100 years, so in 12018.
Since 12018 > 9999, we get a traceback and synchronisation never happens.

opw 1845311

addons/calendar/models/calendar.py

@@ -655,7 +655,13 @@ class Meeting(models.Model):
             }[data['rrule_type']]
 
             deadline = fields.Datetime.from_string(data['stop'])
-            return deadline + relativedelta(**{delay: count * mult})
+            computed_final_date = False
+            while not computed_final_date and count > 0:
+                try:  # may crash if year > 9999 (in case of recurring events)
+                    computed_final_date = deadline + relativedelta(**{delay: count * mult})
+                except ValueError:
+                    count -= data['interval']
+            return computed_final_date or deadline
         return final_date
 
     @api.multi