panic: interface conversion: *core.Node is not gui.IPanel: missing method Cullable

[fxrz12]

Error when clicking Label on new windows：
panic: interface conversion: *core.Node is not gui.IPanel: missing method Cullable

goroutine 1 [running, locked to thread]:
github.com/g3n/engine/gui.(*Window).onMouse(0xc0029fb880, {0x12a7903, 0xc00037f990}, {0x114bcab, 0xc00015da20})
C:/Users/fxrz1/GoProjects/src/github.com/g3n/engine/gui/window.go:144 +0x137
github.com/g3n/engine/core.(*Dispatcher).Dispatch(0xe7bd5d, {0x12a7903, 0xd}, {0x1216d60, 0xc000142070})
C:/Users/fxrz1/GoProjects/src/github.com/g3n/engine/core/dispatcher.go:108 +0xa3
github.com/g3n/engine/gui.sendAncestry({0x133b508, 0xc002afc000}, 0x0, {0x0, 0x0}, {0x0, 0x0}, {0x12a7903, 0xd}, {0x1216d60, ...})
C:/Users/fxrz1/GoProjects/src/github.com/g3n/engine/gui/manager.go:234 +0x144
github.com/g3n/engine/gui.(*manager).onMouse(0xc000178000, {0x12a7903, 0xd}, {0x1216d60, 0xc000142070})
C:/Users/fxrz1/GoProjects/src/github.com/g3n/engine/gui/manager.go:138 +0x177
github.com/g3n/engine/core.(*Dispatcher).Dispatch(0x60037fb80, {0x12a7903, 0xd}, {0x1216d60, 0xc000142070})
C:/Users/fxrz1/GoProjects/src/github.com/g3n/engine/core/dispatcher.go:108 +0xa3
github.com/g3n/engine/window.Init.func3(0x11326c7, 0x0, 0x1, 0x0)
C:/Users/fxrz1/GoProjects/src/github.com/g3n/engine/window/glfw.go:326 +0xb3
github.com/go-gl/glfw/v3.3/glfw.goMouseButtonCB(0xc000186360, 0x0, 0x1, 0x0)
C:/Users/fxrz1/GoProjects/src/github.com/go-gl/glfw/v3.3/glfw/input.go:334 +0x57
github.com/go-gl/glfw/v3.3/glfw._Cfunc_glfwPollEvents()
_cgo_gotypes.go:1517 +0x4e
github.com/go-gl/glfw/v3.3/glfw.PollEvents()
C:/Users/fxrz1/GoProjects/src/github.com/go-gl/glfw/v3.3/glfw/window.go:964 +0x17
github.com/g3n/engine/window.(*GlfwWindow).PollEvents(...)
C:/Users/fxrz1/GoProjects/src/github.com/g3n/engine/window/glfw.go:440
github.com/g3n/engine/app.(*Application).Run(0xc0000221e0, 0xc00037fea0)
C:/Users/fxrz1/GoProjects/src/github.com/g3n/engine/app/app-desktop.go:91 +0x85
main.runApp(0x124d260, 0x0, 0x12a618b)
C:/Users/fxrz1/GoProjects/test/app.go:124 +0x45
main.main()
C:/Users/fxrz1/GoProjects/test/app.go:78 +0x436
AL lib: (EE) alc_cleanup: 1 device not closed

Process finished with the exit code 2
I added the judgment and it was normal：
// Move the window above everything contained in its parent
if _, ok := w.Parent().(IPanel); ok {
parent := w.Parent().(IPanel).GetPanel()
parent.SetTopChild(w)
}
// If the click happened inside the draggable area, then set drag to true
if w.overTop || w.overRight || w.overBottom || w.overLeft {
w.drag = true
Manager().SetCursorFocus(w)
}

[moltzaum]

I also just ran into this issue.

Steps to reproduce:

window := gui.NewWindow(200, 300)
window.SetTitle("Sub-Window")
scene.Add(window)

Click on the bottom-right corner to cause the panic. Tested on Linux too, so its not just a Mac issue.