### 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)

int version_minor = 0;
		int rc = XRRQueryVersion(x11_display, &version_major, &version_minor);
		print_verbose(vformat("Xrandr %d.%d detected.", version_major, version_minor));
		if (rc != 1 || (version_major == 1 && version_minor < 3) || (version_major < 1)) {
			ERR_PRINT("Unsupported Xrandr library version.");
			r_error = ERR_UNAVAILABLE;
			XCloseDisplay(x11_display);
			return;
		}
	}
	{
		int version_major = 0;
		int version_minor = 0;
		int rc = XRenderQueryVersion(x11_display, &version_major, &version_minor);
		print_verbose(vformat("Xrender %d.%d detected.", version_major, version_minor));
		if (rc != 1 || (version_major == 0 && version_minor < 11)) {
			ERR_PRINT("Unsupported Xrender library version.");
			r_error = ERR_UNAVAILABLE;
			XCloseDisplay(x11_display);
			return;
		}
	}
	{
		int version_major = 2; 
		int version_minor = 2;
		int rc = XIQueryVersion(x11_display, &version_major, &version_minor);
		print_verbose(vformat("Xinput %d.%d detected.", version_major, version_minor));
		if (rc != Success || (version_major < 2)) {
			ERR_PRINT("Unsupported Xinput2 library version.");
			r_error = ERR_UNAVAILABLE;