[FIX] google_calendar: default timezone

If no timezone was defined for the user,
the timezone sent to Google for the events
syncrhonization was set as `False` instead
of the right default value `UTC`

opw-660171

addons/google_calendar/google_calendar.py

@@ -236,12 +236,12 @@ class google_calendar(osv.AbstractModel):
             "start": {
                 type: start_date,
                 vstype: None,
-                'timeZone': context.get('tz', 'UTC'),
+                'timeZone': context.get('tz') or 'UTC',
             },
             "end": {
                 type: final_date,
                 vstype: None,
-                'timeZone': context.get('tz', 'UTC'),
+                'timeZone': context.get('tz') or 'UTC',
             },
             "attendees": attendee_list,
             "reminders": {