### Godot version

v4.0 rc6

### System information

Windows 10

### Issue description

When using a ViewportTexture from a SubViewport on a TextureRect, it throws errors after running the scene once and then switching scenes in the editor.
![Pasted image 20230227212626](https://user-images.githubusercontent.com/44676282/221680047-984fa03e-33d1-4856-9a7f-1700b28423cf.png)


### Steps to reproduce

Run the canvas-scene once.
Switch to another scene in the editor.
Switch back to the canvas-scene

### Minimal reproduction project

[ViewportTextureError.zip](https://github.com/godotengine/godot/files/10844099/ViewportTextureError.zip)

SUB_WINDOW_RESIZE_DISABLED,
		SUB_WINDOW_RESIZE_TOP_LEFT,
		SUB_WINDOW_RESIZE_TOP,
		SUB_WINDOW_RESIZE_TOP_RIGHT,
		SUB_WINDOW_RESIZE_LEFT,
		SUB_WINDOW_RESIZE_RIGHT,
		SUB_WINDOW_RESIZE_BOTTOM_LEFT,
		SUB_WINDOW_RESIZE_BOTTOM,
		SUB_WINDOW_RESIZE_BOTTOM_RIGHT,
		SUB_WINDOW_RESIZE_MAX
	};
	struct SubWindow {
		Window *window = nullptr;
		RID canvas_item;
		Rect2i parent_safe_rect;
	};
	
	VRSMode vrs_mode = VRS_DISABLED;
	Ref<Texture2D> vrs_texture;
	struct GUI {
		bool forced_mouse_focus = false; 
		bool mouse_in_viewport = true;
		bool key_event_accepted = false;
		HashMap<int, ObjectID> touch_focus;
		Control *mouse_focus = nullptr;
		Control *last_mouse_focus = nullptr;
		Control *mouse_click_grabber = nullptr;
		BitField<MouseButtonMask> mouse_focus_mask;
		Control *key_focus = nullptr;