### 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)

_THREAD_SAFE_METHOD_
	if (!windows.has(last_focused_window)) {
		return String(); 
	}
	String ret;
	if (!OpenClipboard(windows[last_focused_window].hWnd)) {
		ERR_FAIL_V_MSG("", "Unable to open clipboard.");
	}
	if (IsClipboardFormatAvailable(CF_UNICODETEXT)) {
		HGLOBAL mem = GetClipboardData(CF_UNICODETEXT);
		if (mem != nullptr) {
			LPWSTR ptr = (LPWSTR)GlobalLock(mem);
			if (ptr != nullptr) {
				ret = String::utf16((const char16_t *)ptr);
				GlobalUnlock(mem);