### 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)

bi.bV5Compression = BI_BITFIELDS;
		bi.bV5RedMask = 0x00ff0000;
		bi.bV5GreenMask = 0x0000ff00;
		bi.bV5BlueMask = 0x000000ff;
		bi.bV5AlphaMask = 0xff000000;
		HDC dc = GetDC(nullptr);
		HBITMAP bitmap = CreateDIBSection(dc, reinterpret_cast<BITMAPINFO *>(&bi), DIB_RGB_COLORS, reinterpret_cast<void **>(&buffer), nullptr, 0);
		HBITMAP mask = CreateBitmap(texture_size.width, texture_size.height, 1, 1, nullptr);
		bool fully_transparent = true;
		for (UINT index = 0; index < image_size; index++) {
			int row_index = floor(index / texture_size.width) + atlas_rect.position.y;
			int column_index = (index % int(texture_size.width)) + atlas_rect.position.x;
			if (atlas_texture.is_valid()) {
				column_index = MIN(column_index, atlas_rect.size.width - 1);
				row_index = MIN(row_index, atlas_rect.size.height - 1);
			}
			const Color &c = image->get_pixel(column_index, row_index);
			fully_transparent = fully_transparent && (c.a == 0.f);
			*(buffer + index) = c.to_argb32();
		}
		
		if (cursors[p_shape]) {
			DestroyIcon(cursors[p_shape]);
		}
		if (fully_transparent) {
			cursors[p_shape] = nullptr;
		} else {
			ICONINFO iconinfo;
			iconinfo.fIcon = FALSE;
			iconinfo.xHotspot = p_hotspot.x;