UI related segfault when creating multiple engines with the libf3d

[mwestphal]

Describe the bug
When creating multiple engine, there seems to be some memory related issue

To Reproduce
Steps to reproduce the behavior:

1. Run this python script

import f3d 

def stop_fn(inter):
   inter.stop()

def print_fn():
   print("test")

engine = f3d.Engine.create(False)
inter = engine.interactor
inter.start(1 / 30, partial(stop_fn, inter))
del engine

engine2 = f3d.Engine.create(False)
inter2 = engine2.interactor
inter2.start(1 / 30, print_fn)

2. Press Escape to show console
3. Press Escape to hide console
4. Segfault

../src/python/testing/test_interactor_start.py 
Program received signal SIGSEGV, Segmentation fault.
f3d::detail::interactor_impl::internals::OnConsoleEvent (event=1202, clientData=0x555555bf5e80, data=0x0) at /home/glow/dev/f3d/f3d/src/library/src/interactor_impl.cxx:234
234           self->Options.ui.console = (event == vtkF3DConsoleOutputWindow::ShowEvent);
(gdb) bt
#0  f3d::detail::interactor_impl::internals::OnConsoleEvent (event=1202, clientData=0x555555bf5e80, data=0x0) at /home/glow/dev/f3d/f3d/src/library/src/interactor_impl.cxx:234
#1  0x00007fffedd23a8f in vtkCallbackCommand::Execute (this=0x555555be3020, caller=0x555555a6a8f0, event=1202, callData=0x0) at /home/glow/dev/vtk/vtk1/src/Common/Core/vtkCallbackCommand.cxx:30
#2  0x00007fffede5fd1c in vtkSubjectHelper::InvokeEvent (this=0x555555be3d00, event=1202, callData=0x0, self=0x555555a6a8f0) at /home/glow/dev/vtk/vtk1/src/Common/Core/vtkObject.cxx:638
#3  0x00007fffede602df in vtkObject::InvokeEvent (this=0x555555a6a8f0, event=1202, callData=0x0) at /home/glow/dev/vtk/vtk1/src/Common/Core/vtkObject.cxx:807
#4  0x00007ffff5f02cfa in vtkObject::InvokeEvent (this=0x555555a6a8f0, event=1202) at /home/glow/dev/vtk/vtk1/src/Common/Core/vtkObject.h:223
#5  0x00007ffff5f02363 in vtkF3DImguiConsole::ShowConsole (this=0x555555a6a8f0) at /home/glow/dev/f3d/f3d/src/vtkext/private/module/vtkF3DImguiConsole.cxx:81
#6  0x00007ffff5eff9ff in vtkF3DImguiActor::RenderConsole (this=0x555555c45c60) at /home/glow/dev/f3d/f3d/src/vtkext/private/module/vtkF3DImguiActor.cxx:422
#7  0x00007ffff5ef6f58 in vtkF3DUIActor::RenderOverlay (this=0x555555c45c60, vp=0x555555c63b50) at /home/glow/dev/f3d/f3d/src/vtkext/private/module/vtkF3DUIActor.cxx:114
#8  0x00007ffff40d0691 in vtkDefaultPass::RenderOverlay (this=0x555555ee4ef0, s=0x7fffffffb180) at /home/glow/dev/vtk/vtk1/src/Rendering/OpenGL2/vtkDefaultPass.cxx:175
#9  0x00007ffff40d0044 in vtkDefaultPass::Render (this=0x555555ee4ef0, s=0x7fffffffb180) at /home/glow/dev/vtk/vtk1/src/Rendering/OpenGL2/vtkDefaultPass.cxx:38
#10 0x00007ffff40c5581 in vtkCameraPass::Render (this=0x55555613a950, s=0x7fffffffb180) at /home/glow/dev/vtk/vtk1/src/Rendering/OpenGL2/vtkCameraPass.cxx:133

Expected behavior
No segfault

F3D Information
Paste the content of f3d --version: master