Make POSIX transition rule parser more robust

The POSIX rule parser used by QTzTimeZonePrivate recklessly assumed
that, if splitting the rule on a dot produced more than one part, it
necessarily produced at least three. That's true for well-formed POSIX
rules, but we should catch the case of malformed rules.

Likewise, when calculating the dates of transitions, splitting the
date rule on dots might produce too few fragments; and the fragments
might not parse as valid numbers, or might be out of range for their
respective fields in a date. Check all these cases, too.

Added a test that crashed previously. Changed
QTimeZone::offsetFromUtc() so that its "return zero on invalid"
applies also to the case where the backend returns invalid, in
support of this.

Fixes: QTBUG-92808
Change-Id: Ica383a7a987465483341bdef8dcfd42edb6b43d6
Reviewed-by: Andrei Golubev <andrei.golubev@qt.io>
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>
Reviewed-by: Robert Löhning <robert.loehning@qt.io>
(cherry picked from commit 964f91fd25a59654905c5a68d3cbccedab9ebb5a)
Reviewed-by: Qt Cherry-pick Bot <cherrypick_bot@qt-project.org>

0 files changed, 0 insertions, 0 deletions