### 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)

Hints hints;
			Atom property;
			hints.flags = 2;
			hints.decorations = 0;
			property = XInternAtom(x11_display, "_MOTIF_WM_HINTS", True);
			if (property != None) {
				XChangeProperty(x11_display, wd.x11_window, property, property, 32, PropModeReplace, (unsigned char *)&hints, 5);
			}
		}
		if (wd.is_popup || wd.no_focus) {
			
			Atom type_atom = XInternAtom(x11_display, "_NET_WM_WINDOW_TYPE_UTILITY", False);
			Atom wt_atom = XInternAtom(x11_display, "_NET_WM_WINDOW_TYPE", False);
			if (wt_atom != None && type_atom != None) {
				XChangeProperty(x11_display, wd.x11_window, wt_atom, XA_ATOM, 32, PropModeReplace, (unsigned char *)&type_atom, 1);
			}
		} else {
			Atom type_atom = XInternAtom(x11_display, "_NET_WM_WINDOW_TYPE_NORMAL", False);
			Atom wt_atom = XInternAtom(x11_display, "_NET_WM_WINDOW_TYPE", False);
			if (wt_atom != None && type_atom != None) {
				XChangeProperty(x11_display, wd.x11_window, wt_atom, XA_ATOM, 32, PropModeReplace, (unsigned char *)&type_atom, 1);
			}
		}
		_update_size_hints(id);
#if defined(VULKAN_ENABLED)
		if (context_vulkan) {
			Error err = context_vulkan->window_create(id, p_vsync_mode, wd.x11_window, x11_display, win_rect.size.width, win_rect.size.height);
			ERR_FAIL_COND_V_MSG(err != OK, INVALID_WINDOW_ID, "Can't create a Vulkan window");
		}
#endif