Fix texture using application crash at shutdown

Depending on order things are destroyed at shutdown, texture factory
can get deleted before textures at shutdown. Textures notify factory
at their destructor, which caused the crash.
Changed factory pointer to a guarded one to avoid this.

Change-Id: I032f066a9a77ef92c68c31e0552f880a8f0a90af
Task-number: QTBUG-51045
Reviewed-by: Pasi Keränen <pasi.keranen@theqtcompany.com>

src/imports/qtcanvas3d/teximage3d.cpp

@@ -198,7 +198,7 @@ void CanvasTextureImage::cleanupNetworkReply()
 
 CanvasTextureImage::~CanvasTextureImage()
 {
-    if (m_parentFactory)
+    if (!m_parentFactory.isNull())
         m_parentFactory->handleImageDestroyed(this);
     cleanupNetworkReply();
     delete[] m_pixelCache;
@@ -257,7 +257,8 @@ void CanvasTextureImage::load()
         return;
 
     setImageState(LOADING);
-    m_parentFactory->handleImageLoadingStarted(this);
+    if (!m_parentFactory.isNull())
+        m_parentFactory->handleImageLoadingStarted(this);
     emit imageLoadingStarted(this);
 
     QNetworkRequest request(m_source);

src/imports/qtcanvas3d/teximage3d_p.h

@@ -51,6 +51,7 @@
 #include "abstractobject3d_p.h"
 
 #include <QtCore/QUrl>
+#include <QtCore/QPointer>
 #include <QtGui/QImage>
 #include <QtNetwork/QNetworkAccessManager>
 #include <QtNetwork/QNetworkReply>
@@ -159,7 +160,7 @@ private:
     bool m_pixelCacheFlipY;
     QImage m_glImage;
     QVariant *m_anyValue;
-    CanvasTextureImageFactory *m_parentFactory;
+    QPointer<CanvasTextureImageFactory> m_parentFactory;
 };
 
 QT_CANVAS3D_END_NAMESPACE