### 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)

rendering_device_vulkan = memnew(RenderingDeviceVulkan);
		rendering_device_vulkan->initialize(context_vulkan);
		RendererCompositorRD::make_current();
	}
#endif
	{
		
		XIEventMask all_master_event_mask;
		static unsigned char all_master_mask_data[XIMaskLen(XI_LASTEVENT)] = {};
		all_master_event_mask.deviceid = XIAllMasterDevices;
		all_master_event_mask.mask_len = sizeof(all_master_mask_data);
		all_master_event_mask.mask = all_master_mask_data;
		XISetMask(all_master_event_mask.mask, XI_DeviceChanged);
		XISetMask(all_master_event_mask.mask, XI_RawMotion);
		XISelectEvents(x11_display, DefaultRootWindow(x11_display), &all_master_event_mask, 1);
	}
	cursor_size = XcursorGetDefaultSize(x11_display);
	cursor_theme = XcursorGetTheme(x11_display);
	if (!cursor_theme) {
		print_verbose("XcursorGetTheme could not get cursor theme");
		cursor_theme = "default";
	}
	for (int i = 0; i < CURSOR_MAX; i++) {
		static const char *cursor_file[] = {
			"left_ptr",
			"xterm",
			"hand2",
			"cross",
			"watch",
			"left_ptr_watch",