### 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)

f->get_buffer((uint8_t *)&data_small.write[0], bytecount_small);
	HICON icon_small = CreateIconFromResource((PBYTE)&data_small.write[0], bytecount_small, TRUE, 0x00030000);
	ERR_FAIL_COND_MSG(!icon_small, "Could not create 16x16 @" + itos(small_icon_cc) + " icon, error: " + format_error_message(GetLastError()) + ".");
	
	int err = 0;
	SetLastError(err);
	SendMessage(windows[MAIN_WINDOW_ID].hWnd, WM_SETICON, ICON_SMALL, (LPARAM)icon_small);
	err = GetLastError();
	ERR_FAIL_COND_MSG(err, "Error setting ICON_SMALL: " + format_error_message(err) + ".");
	SendMessage(windows[MAIN_WINDOW_ID].hWnd, WM_SETICON, ICON_BIG, (LPARAM)icon_big);
	err = GetLastError();
	ERR_FAIL_COND_MSG(err, "Error setting ICON_BIG: " + format_error_message(err) + ".");
	memdelete(icon_dir);
}
void DisplayServerWindows::set_icon(const Ref<Image> &p_icon) {
	_THREAD_SAFE_METHOD_
	ERR_FAIL_COND(!p_icon.is_valid());
	if (icon != p_icon) {
		icon = p_icon->duplicate();
		if (icon->get_format() != Image::FORMAT_RGBA8) {
			icon->convert(Image::FORMAT_RGBA8);
		}
	}
	int w = icon->get_width();
	int h = icon->get_height();
	
	int icon_len = 40 + h * w * 4;
	Vector<BYTE> v;
	v.resize(icon_len);
	BYTE *icon_bmp = v.ptrw();