[FIX] calendar: only make leaf evaluation when necessary

A little optimisation to avoid one more query when we have no
recuring event, and only evaluate leaf of recuring event.

addons/calendar/models/calendar.py

@@ -1110,10 +1110,11 @@ class Meeting(models.Model):
             order_fields.append('id')
 
         leaf_evaluations = None
+        recurrent_ids = [meeting.id for meeting in self if meeting.recurrency and meeting.rrule]
         #compose a query of the type SELECT id, condition1 as domain1, condition2 as domaine2
         #This allows to load leaf interpretation of the where clause in one query
         #leaf_evaluations is then used when running custom interpretation of domain for recuring events
-        if self:
+        if self and recurrent_ids:
             select_fields = ["id"]
             where_params_list = []
             for pos, arg in enumerate(domain):
@@ -1124,7 +1125,7 @@ class Meeting(models.Model):
                     where_params_list += where_params
             if len(select_fields) > 1:
                 query = "SELECT %s FROM calendar_event WHERE id in %%s" % (", ".join(select_fields))  # could be improved by only taking event with recurency ?
-                where_params_list += [tuple(self.ids)]
+                where_params_list += [tuple(recurrent_ids)]
                 self._cr.execute(query, where_params_list)
                 leaf_evaluations = dict([(row['id'], row) for row in self._cr.dictfetchall()])
         result_data = []