### 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)

gui.subwindow_over = sw;
						if (!sw->is_input_disabled()) {
							sw->_propagate_window_notification(sw, NOTIFICATION_WM_MOUSE_ENTER);
						}
					}
					if (!sw->is_input_disabled()) {
						sw->_update_mouse_over(sw->get_final_transform().affine_inverse().xform(p_pos - sw->get_position()));
					}
				} else {
					if (gui.subwindow_over) {
						gui.subwindow_over->_mouse_leave_viewport();
						gui.subwindow_over = nullptr;
					}
				}
				return;
			}
		}
		if (gui.subwindow_over) {
			
			gui.subwindow_over->_mouse_leave_viewport();
			gui.subwindow_over = nullptr;
		}
	}
	
	Control *over = gui_find_control(p_pos);
	bool notify_embedded_viewports = false;
	if (over != gui.mouse_over) {
		if (gui.mouse_over) {
			_drop_mouse_over();
		} else {