### 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)

#ifdef GLES3_ENABLED
		if (gl_manager) {
			if (gl_manager->window_create(id, wd.hWnd, hInstance, WindowRect.right - WindowRect.left, WindowRect.bottom - WindowRect.top) != OK) {
				memdelete(gl_manager);
				gl_manager = nullptr;
				windows.erase(id);
				ERR_FAIL_V_MSG(INVALID_WINDOW_ID, "Failed to create an OpenGL window.");
			}
			window_set_vsync_mode(p_vsync_mode, id);
		}
#endif
		RegisterTouchWindow(wd.hWnd, 0);
		DragAcceptFiles(wd.hWnd, true);
		if ((tablet_get_current_driver() == "wintab") && wintab_available) {
			wintab_WTInfo(WTI_DEFSYSCTX, 0, &wd.wtlc);
			wd.wtlc.lcOptions |= CXO_MESSAGES;
			wd.wtlc.lcPktData = PK_STATUS | PK_NORMAL_PRESSURE | PK_TANGENT_PRESSURE | PK_ORIENTATION;
			wd.wtlc.lcMoveMask = PK_STATUS | PK_NORMAL_PRESSURE | PK_TANGENT_PRESSURE;
			wd.wtlc.lcPktMode = 0;
			wd.wtlc.lcOutOrgX = 0;
			wd.wtlc.lcOutExtX = wd.wtlc.lcInExtX;
			wd.wtlc.lcOutOrgY = 0;
			wd.wtlc.lcOutExtY = -wd.wtlc.lcInExtY;
			wd.wtctx = wintab_WTOpen(wd.hWnd, &wd.wtlc, false);
			if (wd.wtctx) {
				wintab_WTEnable(wd.wtctx, true);
				AXIS pressure;
				if (wintab_WTInfo(WTI_DEVICES + wd.wtlc.lcDevice, DVC_NPRESSURE, &pressure)) {
					wd.min_pressure = int(pressure.axMin);
					wd.max_pressure = int(pressure.axMax);