### 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)

for (int i = 0; i < key_event_pos; i++) {
		KeyEvent &ke = key_event_buffer[i];
		switch (ke.uMsg) {
			case WM_CHAR: {
				
				if (!KeyMappingWindows::is_extended_key(ke.wParam) && ((i == 0 && ke.uMsg == WM_CHAR) || (i > 0 && key_event_buffer[i - 1].uMsg == WM_CHAR))) {
					static char32_t prev_wc = 0;
					char32_t unicode = ke.wParam;
					if ((unicode & 0xfffffc00) == 0xd800) {
						if (prev_wc != 0) {
							ERR_PRINT("invalid utf16 surrogate input");
						}
						prev_wc = unicode;
						break; 
					} else if ((unicode & 0xfffffc00) == 0xdc00) {
						if (prev_wc == 0) {
							ERR_PRINT("invalid utf16 surrogate input");
							break; 
						}
						unicode = (prev_wc << 10UL) + unicode - ((0xd800 << 10UL) + 0xdc00 - 0x10000);
						prev_wc = 0;
					} else {
						prev_wc = 0;
					}
					Ref<InputEventKey> k;