### 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)

MDT_Effective_DPI = 0,
	MDT_Angular_DPI = 1,
	MDT_Raw_DPI = 2,
	MDT_Default = MDT_Effective_DPI
};
static int QueryDpiForMonitor(HMONITOR hmon, _MonitorDpiType dpiType = MDT_Default) {
	int dpiX = 96, dpiY = 96;
	static HMODULE Shcore = nullptr;
	typedef HRESULT(WINAPI * GetDPIForMonitor_t)(HMONITOR hmonitor, _MonitorDpiType dpiType, UINT * dpiX, UINT * dpiY);
	static GetDPIForMonitor_t getDPIForMonitor = nullptr;
	if (Shcore == nullptr) {
		Shcore = LoadLibraryW(L"Shcore.dll");
		getDPIForMonitor = Shcore ? (GetDPIForMonitor_t)GetProcAddress(Shcore, "GetDpiForMonitor") : nullptr;
		if ((Shcore == nullptr) || (getDPIForMonitor == nullptr)) {
			if (Shcore) {
				FreeLibrary(Shcore);
			}
			Shcore = (HMODULE)INVALID_HANDLE_VALUE;
		}
	}
	UINT x = 0, y = 0;
	if (hmon && (Shcore != (HMODULE)INVALID_HANDLE_VALUE)) {
		HRESULT hr = getDPIForMonitor(hmon, dpiType , &x, &y);