Fix crash when constructing a QVector with an empty initializer list.

Data::allocate(0) returns a pointer to read-only memory, updating d->size
will segfault. The safety check for this exists in all other QVector ctors
already.

Change-Id: Ida0fe4182de56ee62c7f91e8652cfafbfd7b8410
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>

src/corelib/tools/qvector.h

@@ -438,11 +438,15 @@ QVector<T>::QVector(int asize, const T &t)
 template <typename T>
 QVector<T>::QVector(std::initializer_list<T> args)
 {
+    if (args.size() > 0) {
         d = Data::allocate(args.size());
         // std::initializer_list<T>::iterator is guaranteed to be
         // const T* ([support.initlist]/1), so can be memcpy'ed away from by copyConstruct
         copyConstruct(args.begin(), args.end(), d->begin());
         d->size = int(args.size());
+    } else {
+        d = Data::sharedNull();
+    }
 }
 #endif
 

tests/auto/corelib/tools/qvector/tst_qvector.cpp

@@ -2042,6 +2042,9 @@ void tst_QVector::initializeList()
     QVector<QVector<T>> v3;
     v3 << v1 << (QVector<T>() << val4) << QVector<T>() << v1;
     QCOMPARE(v3, v2);
+
+    QVector<T> v4({});
+    QCOMPARE(v4.size(), 0);
 #endif
 }