QQuickLoader: prevent clearing initial properties after active = true

After commit b6d88c73, we implement the method [disposeInitialPropertyValues]
and clear the cache of initial properties actually. Since we also call this
method after source loaded, it will cause loss of initial properties after
active = true.

Fixes: QTBUG-83895
Change-Id: Iaa500fff14dcaad79a9e68dcbac9f65fa8720456
Reviewed-by: Shawn Rutledge <shawn.rutledge@qt.io>
Reviewed-by: Fabian Kosmale <fabian.kosmale@qt.io>
Reviewed-by: Simon Hausmann <hausmann@gmail.com>

src/quick/items/qquickloader.cpp

@@ -711,7 +711,6 @@ void QQuickLoaderPrivate::incubatorStateChanged(QQmlIncubator::Status status)
     emit q->progressChanged();
     if (status == QQmlIncubator::Ready)
         emit q->loaded();
-    disposeInitialPropertyValues(); // cleanup
 }
 
 void QQuickLoaderPrivate::_q_sourceLoaded()

tests/auto/quick/qquickloader/data/initialPropertyValues.12.qml

@@ -0,0 +1,20 @@
+import QtQuick 2.0
+
+Item {
+    id: root
+    property int i: 0
+
+    Loader {
+        id: loader
+        objectName: "loader"
+        active: false
+    }
+
+    Component.onCompleted: {
+        loader.setSource("CacheClearTest.qml", {i: 12})
+        loader.active = true
+        loader.active = false
+        loader.active = true
+        root.i = loader.item.i // should be 12
+    }
+}

tests/auto/quick/qquickloader/tst_qquickloader.cpp

@@ -698,6 +698,11 @@ void tst_QQuickLoader::initialPropertyValues_data()
                                                                                     << QStringList()
                                                                                     << (QStringList() << "oldi" << "i")
                                                                                     << (QVariantList() << 12 << 42);
+
+    QTest::newRow("ensure initial properties aren't disposed after active = true") << testFileUrl("initialPropertyValues.12.qml")
+            << QStringList()
+            << (QStringList() << "i")
+            << (QVariantList() << 12);
 }
 
 void tst_QQuickLoader::initialPropertyValues()