### 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)

_drop_physics_mouseover();
		}
		gui.mouse_over = over;
		if (over) {
			over->notification(Control::NOTIFICATION_MOUSE_ENTER);
			notify_embedded_viewports = true;
		}
	}
	if (over) {
		SubViewportContainer *c = Object::cast_to<SubViewportContainer>(over);
		if (!c) {
			return;
		}
		Vector2 pos = c->get_global_transform_with_canvas().affine_inverse().xform(p_pos);
		if (c->is_stretch_enabled()) {
			pos /= c->get_stretch_shrink();
		}
		for (int i = 0; i < c->get_child_count(); i++) {
			SubViewport *v = Object::cast_to<SubViewport>(c->get_child(i));
			if (!v || v->is_input_disabled()) {
				continue;
			}
			if (notify_embedded_viewports) {
				v->notification(NOTIFICATION_VP_MOUSE_ENTER);
			}
			v->_update_mouse_over(v->get_final_transform().affine_inverse().xform(pos));
		}
	}
}
void Viewport::_mouse_leave_viewport() {