Fix possible crash with an empty handle

Change-Id: I729c919692c65c0ab4272368b7c98101ef573545
Reviewed-on: http://codereview.qt-project.org/6204
Reviewed-by: Qt Sanity Bot <qt_sanity_bot@ovi.com>
Reviewed-by: Aaron Kennedy <aaron.kennedy@nokia.com>

src/declarative/qml/qdeclarativeproperty.cpp

@@ -1297,7 +1297,7 @@ bool QDeclarativePropertyPrivate::writeBinding(const QDeclarativeProperty &that,
         } \
 
 
-    if (object && pp->valueType.valueTypeCoreIdx == -1) {
+    if (!isUndefined && object && pp->valueType.valueTypeCoreIdx == -1) {
         switch (type) {
         case QMetaType::Int:
             if (result->IsInt32())