Do not store in calendar invalid event

The user could create an event with an end date before the start date during
edition. So event must not be added to the store of GooCalendar because it does
not support such inconsistency.

issue5723
review33291002

tryton/gui/window/view_form/view/calendar_gtk/calendar_.py

@@ -95,6 +95,10 @@ class Calendar_(goocalendar.Calendar):
             elif not end:
                 all_day = True
 
+            # Skip invalid event
+            if end is not None and start > end:
+                continue
+
             # TODO define color code
             label = '\n'.join(record[attrs['name']].get_client(record)
                 for attrs in self.fields).rstrip()