### 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)

Ref<InputEventMouse> me = ev;
	if (me.is_valid()) {
		gui.last_mouse_pos = me->get_position();
		_update_mouse_over();
	}
	if (is_embedding_subwindows() && _sub_windows_forward_input(ev)) {
		set_input_as_handled();
		return;
	}
	if (!_can_consume_input_events()) {
		return;
	}
	if (!is_input_handled()) {
		ERR_FAIL_COND(!is_inside_tree());
		get_tree()->_call_input_pause(input_group, SceneTree::CALL_INPUT_TYPE_INPUT, ev, this); 
	}
	if (!is_input_handled()) {
		ERR_FAIL_COND(!is_inside_tree());
		_gui_input_event(ev);
	} else {
		
		_gui_cleanup_internal_state(ev);
	}
	if (!is_input_handled()) {
		_push_unhandled_input_internal(ev);
	}
	event_count++;
}
#ifndef DISABLE_DEPRECATED
void Viewport::push_unhandled_input(const Ref<InputEvent> &p_event, bool p_local_coords) {