### 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)

wd.xic = XCreateIC(xim,
						XNInputStyle, xim_style,
						XNClientWindow, wd.x11_xim_window,
						XNFocusWindow, wd.x11_xim_window,
						XNPreeditAttributes, preedit_attributes,
						(char *)nullptr);
				XFree(preedit_attributes);
			} else {
				wd.xic = XCreateIC(xim,
						XNInputStyle, xim_style,
						XNClientWindow, wd.x11_xim_window,
						XNFocusWindow, wd.x11_xim_window,
						(char *)nullptr);
			}
			if (XGetICValues(wd.xic, XNFilterEvents, &im_event_mask, nullptr) != nullptr) {
				WARN_PRINT("XGetICValues couldn't obtain XNFilterEvents value");
				XDestroyIC(wd.xic);
				wd.xic = nullptr;
			}
			if (wd.xic) {
				XUnsetICFocus(wd.xic);
			} else {
				WARN_PRINT("XCreateIC couldn't create wd.xic");
			}
		} else {
			wd.xic = nullptr;
			WARN_PRINT("XCreateIC couldn't create wd.xic");
		}
		_update_context(wd);
		if (p_flags & WINDOW_FLAG_BORDERLESS_BIT) {