QML: Fortify qmlExecuteDeferred some more

I don't know how to trigger this, but a recent crash report from the CI
shows that we can get there without a valid engine.

Pick-to: 6.5
Change-Id: I9f17894da82b8e7eab88181c96dfa8eaf7795523
Reviewed-by: Fabian Kosmale <fabian.kosmale@qt.io>

1 files changed, 14 insertions, 8 deletions

diff --git a/src/qml/qml/qqml.cpp b/src/qml/qml/qqml.cpp
index 6140a532f1..13654d0cb0 100644
--- a/src/qml/qml/qqml.cpp
+++ b/src/qml/qml/qqml.cpp
@@ -50,17 +50,23 @@ void qmlExecuteDeferred(QObject *object)
 {
     QQmlData *data = QQmlData::get(object);
 
-    if (data && !data->deferredData.isEmpty() && !data->wasDeleted(object)) {
-        QQmlEnginePrivate *ep = QQmlEnginePrivate::get(data->context->engine());
+    if (!data
+            || !data->context
+            || !data->context->engine()
+            || data->deferredData.isEmpty()
+            || data->wasDeleted(object)) {
+        return;
+    }
 
-        QQmlComponentPrivate::DeferredState state;
-        QQmlComponentPrivate::beginDeferred(ep, object, &state);
+    QQmlEnginePrivate *ep = QQmlEnginePrivate::get(data->context->engine());
 
-        // Release the reference for the deferral action (we still have one from construction)
-        data->releaseDeferredData();
+    QQmlComponentPrivate::DeferredState state;
+    QQmlComponentPrivate::beginDeferred(ep, object, &state);
 
-        QQmlComponentPrivate::completeDeferred(ep, &state);
-    }
+    // Release the reference for the deferral action (we still have one from construction)
+    data->releaseDeferredData();
+
+    QQmlComponentPrivate::completeDeferred(ep, &state);
 }
 
 QQmlContext *qmlContext(const QObject *obj)