It's possible, as was (and still is) documented, at least on Windows,
for the backend to determine the system local time zone's properties
but not its IANA ID. (That involves an update to Windows introducing a
Windows zone ID unknown to the CLDR with whose data Qt was compiled.)
Formerly this lead to systemTimeZoneId() and systemTimeZone().id()
being inconsistent. Furthermore, either in this case or when the
system zone can't be determined, passing the return from
systemTimeZoneId() to the constructor got a valid QTimeZone that did
not faithfully represent the system's local time or the return from
systemTimeZone().
[ChangeLog][QtCore][QTimeZone] When unable to determine the IANA ID of
the system's local time zone, QTimeZone::systemTimeZoneId() now
returns empty instead of the "UTC" it formerly, and misleadingly,
returned. Passing the return to the QTimeZone constructor now
consistently produces the same as calling QTimeZone::systemTimeZone(),
whose id() now matches the return from QTimeZone::systemTimeZoneId().
This is independent of whether QTimeZone::systemTimeZone() is valid.
Change-Id: I55bbe3ea407ca38343a09da353d9336708747bf1
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>
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