QQuickPainterItem memory leak when update is called on iOS

Hi,

I believe I have discovered a memory leak on QQuickPaintedItem on iOS. I was having a huge memory increase on iOS, something that I couldn't observe on Windows or OSX (didn't test on Android yet). 

In my applications I use QQuickPaintedItem for custom graphics a lot. After commenting a lot of code of my application I have isolated the problem. 

Attached is a simple project that illustrates how QQuickPaintedItem starts growing in memory usage second by second when update is being called.

If update() inside the timerEvent is not called, the memory does not grow.

To test, run qmake on this project and generate the xcode project:

~/Qt/5.12.6/ios/bin/qmake ~/workspace/painteditembug/painteditembug.pro

and then run and check the memory usage panel.

Them, run the same example but with line 9 of PaintedItem.cpp commented out.

Let me know if you need further information.

Best regards,

Nuno