### Godot version

Godot Engine v4.0.stable.official.92bee43ad

### System information

Windows 10

### Issue description

The documentation states that passing ```null``` into the image parameter of ```set_custom_mouse_cursor``` will change it back to the system cursor, however I find that it removes the cursor's image entirely, rather than setting it to the system's cursor.


### Steps to reproduce

```var isimage = false
var theimage = load("res://final.png")

func _on_my_button_pressed():
    if isimage == false:
        Input.set_custom_mouse_cursor(theimage, Input.CURSOR_ARROW, Vector2(16,16))
        isimage = true
        
    else:
        Input.set_custom_mouse_cursor(null)
        isimage = false```

When the button is pressed, the cursor is meant to change to the new cursor. When it has been pressed a second time, it changes back to the default cursor. However, upon pressing it a second time, it simply disappears. The cursor becomes visible again when the cursor exits and re-enters the window.

### Minimal reproduction project

[null mouse.zip](https://github.com/godotengine/godot/files/10901969/null.mouse.zip)

for (KeyValue<WindowID, WindowData> &E : windows) {
#ifdef VULKAN_ENABLED
		if (context_vulkan) {
			context_vulkan->window_destroy(E.key);
		}
#endif
#ifdef GLES3_ENABLED
		if (gl_manager) {
			gl_manager->window_destroy(E.key);
		}
#endif
		WindowData &wd = E.value;
		if (wd.xic) {
			XDestroyIC(wd.xic);
			wd.xic = nullptr;
		}
		XDestroyWindow(x11_display, wd.x11_xim_window);
#ifdef XKB_ENABLED
		if (xkb_loaded_v05p) {
			if (wd.xkb_state) {
				xkb_compose_state_unref(wd.xkb_state);
				wd.xkb_state = nullptr;
			}
		}
#endif
		XUnmapWindow(x11_display, wd.x11_window);
		XDestroyWindow(x11_display, wd.x11_window);
	}
#ifdef XKB_ENABLED