[FIX] calendar: recurring events

Do not parse the rule with `rrulestr`, because converting back to string
will change the original rule.

addons/calendar/models/calendar.py

@@ -1757,8 +1757,6 @@ class Meeting(models.Model):
     def _fix_rrule(self, values):
         rule_str = values.get('rrule')
         if rule_str:
-            rule = rrule.rrulestr(rule_str)
-            if not rule._until and not rule._count:
-                rule._count = 100
-                rule_str = str(rule).split('RRULE:')[-1]
+            if 'UNTIL' not in rule_str and 'COUNT' not in rule_str:
+                rule_str += ';COUNT=100'
         return rule_str