### Godot version

4.0.dev (c309de53997feff3286295fb2d71657f112a15db)

### System information

Linux, Nvidia, Vulkan

### Issue description

Editor segfaults when certain conditions are met when using the AnimationPlayer editor.

### Steps to reproduce

1. Create multiple animations, saved into a animation collection
2. Open an existing animation, then make a new empty animation
3. Change from seconds to fps, or add a new property to animate ()
4. Editor crashes

NOTE: It is slightly random and I have not found a perfect repro

### Minimal reproduction project

N/A (TBD?)
EditorNode::get_singleton()->show_warning(
			TTR("This animation belongs to an imported scene, so changes to imported tracks will not be saved.\n\nTo modify this animation, navigate to the scene's Advanced Import settings and select the animation.\nSome options, including looping, are available here. To add custom tracks, enable \"Save To File\" and\n\"Keep Custom Tracks\"."),
			TTR("Warning: Editing imported animation"));
}
void AnimationTrackEditor::_select_all_tracks_for_copy() {
	TreeItem *track = track_copy_select->get_root()->get_first_child();
	if (!track) {
		return;
	}
	bool all_selected = true;
	while (track) {
		if (!track->is_checked(0)) {
			all_selected = false;
		}
		track = track->get_next();
	}
	track = track_copy_select->get_root()->get_first_child();
	while (track) {
		track->set_checked(0, !all_selected);
		track = track->get_next();
	}
}
void AnimationTrackEditor::_bind_methods() {