### 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?)
AnimationPlayer *player = AnimationPlayerEditor::get_singleton()->get_player();
	if (player->has_animation(SceneStringNames::get_singleton()->RESET)) {
		return player->get_animation(SceneStringNames::get_singleton()->RESET);
	} else {
		Ref<AnimationLibrary> al;
		if (!player->has_animation_library("")) {
			al.instantiate();
			player->add_animation_library("", al);
		} else {
			al = player->get_animation_library("");
		}
		Ref<Animation> reset_anim;
		reset_anim.instantiate();
		reset_anim->set_length(ANIM_MIN_LENGTH);
		EditorUndoRedoManager *undo_redo = EditorUndoRedoManager::get_singleton();
		undo_redo->add_do_method(al.ptr(), "add_animation", SceneStringNames::get_singleton()->RESET, reset_anim);
		undo_redo->add_do_method(AnimationPlayerEditor::get_singleton(), "_animation_player_changed", player);
		undo_redo->add_undo_method(al.ptr(), "remove_animation", SceneStringNames::get_singleton()->RESET);
		undo_redo->add_undo_method(AnimationPlayerEditor::get_singleton(), "_animation_player_changed", player);
		return reset_anim;
	}
}
void AnimationTrackEditor::_confirm_insert_list() {