### 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)

_THREAD_SAFE_METHOD_
	ERR_FAIL_COND(!windows.has(p_window));
	WindowData &wd = windows[p_window];
	switch (p_flag) {
		case WINDOW_FLAG_RESIZE_DISABLED: {
			wd.resizable = !p_enabled;
			_update_window_style(p_window);
		} break;
		case WINDOW_FLAG_BORDERLESS: {
			wd.borderless = p_enabled;
			_update_window_style(p_window);
			_update_window_mouse_passthrough(p_window);
			ShowWindow(wd.hWnd, (wd.no_focus || wd.is_popup) ? SW_SHOWNOACTIVATE : SW_SHOW); 
		} break;
		case WINDOW_FLAG_ALWAYS_ON_TOP: {
			ERR_FAIL_COND_MSG(wd.transient_parent != INVALID_WINDOW_ID && p_enabled, "Transient windows can't become on top");
			wd.always_on_top = p_enabled;
			_update_window_style(p_window);
		} break;
		case WINDOW_FLAG_TRANSPARENT: {
			if (p_enabled) {
				
				DWM_BLURBEHIND bb;
				ZeroMemory(&bb, sizeof(bb));
				HRGN hRgn = CreateRectRgn(0, 0, -1, -1);
				bb.dwFlags = DWM_BB_ENABLE | DWM_BB_BLURREGION;
				bb.hRgnBlur = hRgn;
				bb.fEnable = TRUE;
				DwmEnableBlurBehindWindow(wd.hWnd, &bb);
				wd.layered_window = true;