### 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)

DisplayServerWindows *ds_win = static_cast<DisplayServerWindows *>(DisplayServer::get_singleton());
	if (ds_win) {
		return ds_win->MouseProc(code, wParam, lParam);
	} else {
		return ::CallNextHookEx(nullptr, code, wParam, lParam);
	}
}
DisplayServer::WindowID DisplayServerWindows::window_get_active_popup() const {
	const List<WindowID>::Element *E = popup_list.back();
	if (E) {
		return E->get();
	} else {
		return INVALID_WINDOW_ID;
	}
}
void DisplayServerWindows::window_set_popup_safe_rect(WindowID p_window, const Rect2i &p_rect) {
	_THREAD_SAFE_METHOD_
	ERR_FAIL_COND(!windows.has(p_window));
	WindowData &wd = windows[p_window];
	wd.parent_safe_rect = p_rect;
}
Rect2i DisplayServerWindows::window_get_popup_safe_rect(WindowID p_window) const {
	_THREAD_SAFE_METHOD_
	ERR_FAIL_COND_V(!windows.has(p_window), Rect2i());
	const WindowData &wd = windows[p_window];
	return wd.parent_safe_rect;
}
void DisplayServerWindows::popup_open(WindowID p_window) {