Correct a misguided assertion in QTzTimeZonePrivate

Without ICU, the TZ-DB backend for time-zones tripped over an
assertion when running tst_QTimeZone::stressTest(), which happened to
probe a zone between its last transition and the first transition of a
POSIX rule that followed it.  The code assumed there was no interval
between these two; apparently, there can be.

Change-Id: I3d0ad41fec0a255db2f9bfac54d33aa9b83938e8
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>

1 files changed, 4 insertions, 2 deletions

diff --git a/src/corelib/tools/qtimezoneprivate_tz.cpp b/src/corelib/tools/qtimezoneprivate_tz.cpp
index bed62a02bd..fa4ec031fa 100644
--- a/src/corelib/tools/qtimezoneprivate_tz.cpp
+++ b/src/corelib/tools/qtimezoneprivate_tz.cpp
@@ -1022,8 +1022,10 @@ QTimeZonePrivate::Data QTzTimeZonePrivate::previousTransition(qint64 beforeMSecs
                                        [beforeMSecsSinceEpoch] (const QTimeZonePrivate::Data &at) {
                                            return at.atMSecsSinceEpoch < beforeMSecsSinceEpoch;
                                        });
-        Q_ASSERT(it > posixTrans.cbegin());
-        return *--it;
+        if (it > posixTrans.cbegin())
+            return *--it;
+        // else: it fell between the last transition and the first of the POSIX rule.
+        return dataForTzTransition(m_tranTimes.last());
     }
 
     // Otherwise if we can find a valid tran then use its rule