Avoid leaking the QPlatformTextureList

Task-number: QTBUG-45395
Change-Id: I8fbdc5136d7d15b9c131d6b91186a1bf2645e4d4
Reviewed-by: Jørgen Lind <jorgen.lind@theqtcompany.com>

src/widgets/kernel/qwidgetbackingstore.cpp

@@ -762,6 +762,7 @@ QWidgetBackingStore::~QWidgetBackingStore()
         resetWidget(dirtyRenderToTextureWidgets.at(c));
 
 #ifndef QT_NO_OPENGL
+    delete widgetTextures;
     delete dirtyOnScreenWidgets;
 #endif
     dirtyOnScreenWidgets = 0;