### 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)

KeyMappingWindows::initialize();
	drop_events = false;
	key_event_pos = 0;
	alt_mem = false;
	gr_mem = false;
	shift_mem = false;
	control_mem = false;
	meta_mem = false;
	hInstance = static_cast<OS_Windows *>(OS::get_singleton())->get_hinstance();
	pressrc = 0;
	old_invalid = true;
	mouse_mode = MOUSE_MODE_VISIBLE;
	rendering_driver = p_rendering_driver;
	
	tts = memnew(TTS_Windows);
	
	screen_set_keep_on(GLOBAL_GET("display/window/energy_saving/keep_screen_on"));
	
	OSVERSIONINFOW os_ver;
	ZeroMemory(&os_ver, sizeof(OSVERSIONINFOW));
	os_ver.dwOSVersionInfoSize = sizeof(OSVERSIONINFOW);
	HMODULE nt_lib = LoadLibraryW(L"ntdll.dll");
	if (nt_lib) {
		RtlGetVersionPtr RtlGetVersion = (RtlGetVersionPtr)GetProcAddress(nt_lib, "RtlGetVersion");
		if (RtlGetVersion) {