### 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)

#include <sys/types.h>
#include <unistd.h>
#undef CursorShape
#include <X11/XKBlib.h>
#define WM_NormalState 1L  window normal state
#define WM_IconicState 3L  window minimized
#define _NET_WM_STATE_REMOVE 0L  remove/unset property
#define _NET_WM_STATE_ADD 1L  add/set property
#define XINPUT_CLIENT_VERSION_MAJOR 2
#define XINPUT_CLIENT_VERSION_MINOR 2
#define VALUATOR_ABSX 0
#define VALUATOR_ABSY 1
#define VALUATOR_PRESSURE 2
#define VALUATOR_TILTX 3
#define VALUATOR_TILTY 4
#ifdef DISPLAY_SERVER_X11_DEBUG_LOGS_ENABLED
#define DEBUG_LOG_X11(...) printf(__VA_ARGS__)
#else
#define DEBUG_LOG_X11(...)
#endif
static const double abs_resolution_mult = 10000.0;
static const double abs_resolution_range_mult = 10.0;
struct Hints {
	unsigned long flags = 0;
	unsigned long functions = 0;
	unsigned long decorations = 0;
	long inputMode = 0;
	unsigned long status = 0;
};
static String get_atom_name(Display *p_disp, Atom p_atom) {