Don't crash: Connections with a signal on a nonexistent object

Task-number: QTBUG-56551
Change-Id: Ide09f177d3f6a3e9902f8ea904b3e6e4b998bd39
Reviewed-by: Jan Arve Sæther <jan-arve.saether@qt.io>
(cherry picked from commit 02830aa)
Reviewed-by: Lars Knoll <lars.knoll@qt.io>

src/qml/qml/qqmlpropertycache.cpp

@@ -1067,8 +1067,11 @@ int QQmlPropertyCache::originalClone(QObject *object, int index)
     QQmlData *data = QQmlData::get(object, false);
     if (data && data->propertyCache) {
         QQmlPropertyCache *cache = data->propertyCache;
-        while (cache->signal(index)->isCloned())
+        QQmlPropertyData *sig = cache->signal(index);
+        while (sig && sig->isCloned()) {
             --index;
+            sig = cache->signal(index);
+        }
     } else {
         while (QMetaObjectPrivate::signal(object->metaObject(), index).attributes() & QMetaMethod::Cloned)
             --index;

tests/auto/quick/qquickitem2/data/nonexistentPropertyConnection.qml

@@ -0,0 +1,11 @@
+import QtQuick 2.4
+
+Item {
+    function hint() {
+    }
+
+    Connections {
+        target: BlaBlaBla
+        onHint: hint();
+    }
+}

tests/auto/quick/qquickitem2/tst_qquickitem.cpp

@@ -101,6 +101,7 @@ private slots:
     void mapCoordinatesRect();
     void mapCoordinatesRect_data();
     void propertyChanges();
+    void nonexistentPropertyConnection();
     void transforms();
     void transforms_data();
     void childrenRect();
@@ -2588,6 +2589,15 @@ void tst_QQuickItem::propertyChanges()
     delete window;
 }
 
+void tst_QQuickItem::nonexistentPropertyConnection()
+{
+    // QTBUG-56551: don't crash
+    QQmlComponent component(&engine, testFileUrl("nonexistentPropertyConnection.qml"));
+    QObject *o = component.create();
+    QVERIFY(o);
+    delete o;
+}
+
 void tst_QQuickItem::childrenRect()
 {
     QQuickView *window = new QQuickView(0);