Those QTimeZones failed to convert to other timezones because the data()
virtual function was never overridden and reimplemented. That meant all
QUtcTimeZonePrivate objects were *really* UTC, with no offset.
Task-number: QTBUG-44600
Change-Id: Ia0aac2f09e9245339951ffff13c5294bb783c674
Reviewed-by: Marc Mutz <marc.mutz@kdab.com>