Very often bad values for events created without start time or end time

Default events are without time since #1569.

Events without time should start at 00:00 and end at 23:59.

Now, it is not always the case.

It causes problems for comparaison request.

For example : an event today (begins and ends at 2024-11-22) is not surely displayed on a group page because end time can be before now.

If it is 19:00 and event start time is 00:00 and event end time is 01:00, the event is wrongly not displayed on the event section on group page.