### 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)

k.instantiate();
					Key keycode = KeyMappingWindows::get_keysym(MapVirtualKey((ke.lParam >> 16) & 0xFF, MAPVK_VSC_TO_VK));
					Key key_label = keycode;
					Key physical_keycode = KeyMappingWindows::get_scansym((ke.lParam >> 16) & 0xFF, ke.lParam & (1 << 24));
					static BYTE keyboard_state[256];
					memset(keyboard_state, 0, 256);
					wchar_t chars[256] = {};
					UINT extended_code = MapVirtualKey((ke.lParam >> 16) & 0xFF, MAPVK_VSC_TO_VK_EX);
					if (!(ke.lParam & (1 << 24)) && ToUnicodeEx(extended_code, (ke.lParam >> 16) & 0xFF, keyboard_state, chars, 255, 4, GetKeyboardLayout(0)) > 0) {
						String keysym = String::utf16((char16_t *)chars, 255);
						if (!keysym.is_empty()) {
							key_label = fix_key_label(keysym[0], keycode);
						}
					}
					k->set_window_id(ke.window_id);
					if (keycode != Key::SHIFT) {
						k->set_shift_pressed(ke.shift);
					}
					if (keycode != Key::ALT) {
						k->set_alt_pressed(ke.alt);
					}
					if (keycode != Key::CTRL) {
						k->set_ctrl_pressed(ke.control);
					}
					if (keycode != Key::META) {
						k->set_meta_pressed(ke.meta);
					}
					k->set_pressed(true);
					k->set_keycode(keycode);
					k->set_physical_keycode(physical_keycode);