[GUI] Invalidate static dangling pointer

[alxbilger]

Consider the following Python script:

# Required import for SOFA within python
import Sofa

# Import the GUI package
import SofaImGui
import Sofa.Gui

def main():
    # Call the SOFA function to create the root node
    root = Sofa.Core.Node("root")

    # Call the createScene function, as runSofa does
    createScene(root)

    # Once defined, initialization of the scene graph
    Sofa.Simulation.initRoot(root)

    # Launch the GUI (imgui is now by default, to use Qt please refer to the example "basic-useQtGui.py")
    Sofa.Gui.GUIManager.Init("myscene", "imgui")
    Sofa.Gui.GUIManager.createGUI(root, __file__)
    Sofa.Gui.GUIManager.SetDimension(1080, 800)

    # Initialization of the scene will be done here
    Sofa.Gui.GUIManager.MainLoop(root)
    Sofa.Gui.GUIManager.closeGUI()

def createScene(rootNode):
    #Doesn't do anything yet
    return rootNode

if __name__ == '__main__':
    # Note the 2 calls to main()
    main()
    main()

In the same program, we open twice a new GUI. After closing the first GUI, the static pointer to a GUI is dangling. It must be reinitialized to nullptr for a proper behavior (otherwise it crashes).

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Reviewers will merge this pull-request only if

• it builds with SUCCESS for all platforms on the CI.
• it does not generate new warnings.
• it does not generate new unit test failures.
• it does not generate new scene test failures.
• it does not break API compatibility.
• it is more than 1 week old (or has fast-merge label).

[bakpaul]

Don't we also need to delete the pointer ? Otherwise we have memory leak

[alxbilger]

No, it's not the responsibility of GUIManager. Each GUI destroys itself