Fix: application might segfault at exit

[ThisALV]

There is two bugs that sometimes caused a segfault when application exits :

• The foreach loops on deletionPool, when deleting a view, might inserts other views inside the deletionPool set by calling Box destructor, resulting in undefined behavior. To avoid this, the set is can be replaced by a queue. I added required checks in addToFreeQueue to avoid queuing the same view twice.
• AppletFrameItem destructor isn't checking if hintView is ptr locked before deletion. At application exit it sometimes caused hintView to be deleted twice causing a Segfault.

[xfangfang]

@ThisALV Could you please provide a demo code about how to trigger this deletionPool bug?

@XITRIX do you have any thoughts on that?

[XITRIX]

It looks like a quite reasonable fix, but it’s almost 2am and I need to sleep. Tomorrow I’ll try to review it properly

[XITRIX]

Looks like a really nice PR, could you please change this small things and will look perfect to me?

[ThisALV]

Looks like a really nice PR, could you please change this small things and will look perfect to me?

Sure, I'm not near my computer rn but I'll push a commit in a few hours

[ThisALV]

@ThisALV Could you please provide a demo code about how to trigger this deletionPool bug?

@XITRIX do you have any thoughts on that?

To reproduce the bug :

In pokemon_view.cpp line 55 was commented out, De-comment it, replace it by getAppletFrameItem()->setHintView(holder); and set global quit to true in the main function, then inside the app, open a pokemon view in the pokedex and press + to quit the app while the pokemon view is displayed, it should segfault.

It seems closing the app while a hintview is displayed was triggering the segfault before the fix, explaining why it was commented out in the demo app

[ThisALV]

Looks like a really nice PR, could you please change this small things and will look perfect to me?

Commit done