[FIX] admin calendar : validate custom flags value

From admin calendar, when you want to create a calendar, there is an exception at the customstatus field level. After analysis of the error message, we notice that the constraint of the field, only one character can be recorded, y or n, otherwise there will be an exception. So because of this, we find it better to validate all the elements of the customflags since they have the same constraint. Task: https://avan.tech/item68774-Fix-all-errors-in-logs-that-are-not-related-to-Cypht-Webmail-Smarty-icons-and-menus-was-Use-the-GlitchTip-error-reporting-as-a-perpetual-to-do-list-for-junior-developers#threadId=63594 Issiue Glitchtip: https://app.glitchtip.com/evoludata/issues/1856068