### Godot version

v4.0.beta17.mono.official [c40020513]

### System information

Windows 11 22H2

### Issue description

If a focused subwindow is destroyed, DisplayServerWindows may still attempt to send mouse motion events to that window, because `last_focused_window` isn't updated until another window is focused.

```
ERROR: Condition "!windows.has(p_window)" is true. Returning: Point2i()
   at: window_get_position (platform/windows/display_server_windows.cpp:999)
```

### Steps to reproduce

Run the MRP, click some non-Godot application window to focus it, then click the "CLOSE" button in the secondary window. This destroys the window without re-focusing the main window, so hovering the mouse over the main window will produce the error message above.

### Minimal reproduction project

[native_windows_hover.zip](https://github.com/godotengine/godot/files/10573386/native_windows_hover.zip)

DisplayServer *ds = memnew(DisplayServerWindows(p_rendering_driver, p_mode, p_vsync_mode, p_flags, p_position, p_resolution, p_screen, r_error));
	if (r_error != OK) {
		if (p_rendering_driver == "vulkan") {
			String executable_name = OS::get_singleton()->get_executable_path().get_file();
			OS::get_singleton()->alert(
					vformat("Your video card drivers seem not to support the required Vulkan version.\n\n"
							"If possible, consider updating your video card drivers or using the OpenGL 3 driver.\n\n"
							"You can enable the OpenGL 3 driver by starting the engine from the\n"
							"command line with the command:\n'%s --rendering-driver opengl3'\n\n"
							"If you have recently updated your video card drivers, try rebooting.",
							executable_name),
					"Unable to initialize Vulkan video driver");
		} else {
			OS::get_singleton()->alert(
					"Your video card drivers seem not to support the required OpenGL 3.3 version.\n\n"
					"If possible, consider updating your video card drivers.\n\n"
					"If you have recently updated your video card drivers, try rebooting.",
					"Unable to initialize OpenGL video driver");
		}
	}
	return ds;
}
void DisplayServerWindows::register_windows_driver() {