### 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)

XChangeProperty(x11_display, wd.x11_window, xdnd_aware, XA_ATOM, 32, PropModeReplace, (unsigned char *)&xdnd_version, 1);
		}
		if (xim && xim_style) {
			
			
			MutexLock mutex_lock(events_mutex);
			
			if ((xim_style & XIMPreeditPosition) != 0) {
				xim_style &= ~XIMPreeditPosition;
				xim_style |= XIMPreeditCallbacks;
			}
			if ((xim_style & XIMPreeditCallbacks) != 0) {
				::XIMCallback preedit_start_callback;
				preedit_start_callback.client_data = (::XPointer)(this);
				preedit_start_callback.callback = (::XIMProc)(void *)(_xim_preedit_start_callback);
				::XIMCallback preedit_done_callback;
				preedit_done_callback.client_data = (::XPointer)(this);
				preedit_done_callback.callback = (::XIMProc)(_xim_preedit_done_callback);
				::XIMCallback preedit_draw_callback;
				preedit_draw_callback.client_data = (::XPointer)(this);
				preedit_draw_callback.callback = (::XIMProc)(_xim_preedit_draw_callback);
				::XIMCallback preedit_caret_callback;
				preedit_caret_callback.client_data = (::XPointer)(this);
				preedit_caret_callback.callback = (::XIMProc)(_xim_preedit_caret_callback);
				::XVaNestedList preedit_attributes = XVaCreateNestedList(0,
						XNPreeditStartCallback, &preedit_start_callback,
						XNPreeditDoneCallback, &preedit_done_callback,
						XNPreeditDrawCallback, &preedit_draw_callback,
						XNPreeditCaretCallback, &preedit_caret_callback,
						(char *)nullptr);