### 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)

use_prime = 0;
					}
				}
			}
			if (use_prime == -1) {
				print_verbose("Detecting GPUs, set DRI_PRIME in the environment to override GPU detection logic.");
				use_prime = detect_prime();
			}
			if (use_prime) {
				print_line("Found discrete GPU, setting DRI_PRIME=1 to use it.");
				print_line("Note: Set DRI_PRIME=0 in the environment to disable Godot from using the discrete GPU.");
				setenv("DRI_PRIME", "1", 1);
			}
		}
		GLManager_X11::ContextType opengl_api_type = GLManager_X11::GLES_3_0_COMPATIBLE;
		gl_manager = memnew(GLManager_X11(p_resolution, opengl_api_type));
		if (gl_manager->initialize(x11_display) != OK) {
			memdelete(gl_manager);
			gl_manager = nullptr;
			r_error = ERR_UNAVAILABLE;
			return;
		}
		driver_found = true;
		if (true) {
			RasterizerGLES3::make_current();
		} else {
			memdelete(gl_manager);
			gl_manager = nullptr;
			r_error = ERR_UNAVAILABLE;
			return;