Stealth checkpoints persist between quests

[wjt]

Steps to reproduce:

• Play the template StoryQuest
• Now play the LoreQuest up to the stealth level

Expected result:

• Player starts at the beginning of the stealth level

Actual result:

• Player starts at the first checkpoint

I believe this is because the checkpoint is stored in the game state as the next spawn point, but this is not cleared when changing to a new scene, and the node path happens to match.

[wjt]

threadbare/scenes/globals/scene_switcher/scene_switcher.gd

Lines 105 to 109 in dfd5e06

	func change_to_packed(scene: PackedScene, spawn_point: NodePath = ^"") -> void:
	if get_tree().change_scene_to_packed(scene) == OK:
	_set_hash(scene.resource_path)
	if spawn_point != ^"":
	GameState.current_spawn_point = spawn_point

I think we can simply unconditionally set GameState.current_spawn_point here, even if the supplied path is empty ^""