[FIX] set timezone on context if empty in event and user

Prior to this commit, synchronizing an event to the CalDAV server could
break in the _add_event_dates method if both self.event_tz and
self.env.user.tz were empty (False). This should be a rare occurrence,
but adding a fallback of self._context.get('tz') should help.

caldav_sync/__manifest__.py

@@ -8,7 +8,7 @@
 
 {
     "name": "CalDAV Synchronization",
-    "version": "17.0.0.6.0",
+    "version": "17.0.0.6.1",
     "license": "LGPL-3",
     "category": "Productivity",
     "summary": "Synchronize Odoo Calendar Events with CalDAV Servers",

caldav_sync/models/calendar_event.py

@@ -453,7 +453,7 @@ class CalendarEvent(models.Model):
 
     def _add_event_dates(self, event_data: Dict) -> None:
         """Add pertinent dates to event data, based on self."""
-        tz = self.event_tz or self.env.user.tz
+        tz = self.event_tz or self.env.user.tz or self._context.get('tz')
         event_tz = timezone(tz)
         event_data["last-modified"] = vDatetime(
             utc.localize(self.write_date).astimezone(event_tz)