[FIX] calendar: all day event

- Set the TZ as 'America/Martinique'
- In the calendar (month view), click on a date D.
- Fill in the topic, then click on "Edit"

The date is set to D-1.

Commit 09066fbb makes the date consistent when the user sets an
event as an all day event by taking into account the appropriate
timezone.

However, in the case of an event created from the month view, this TZ
modification should not be applied.

opw-766638