### 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)

ImmSetCandidateWindow(windows[window_id].im_himc, &cf);
			cf.dwStyle = CFS_EXCLUDE;
			cf.rcArea.left = windows[window_id].im_position.x;
			cf.rcArea.right = windows[window_id].im_position.x;
			cf.rcArea.top = windows[window_id].im_position.y;
			cf.rcArea.bottom = windows[window_id].im_position.y;
			ImmSetCandidateWindow(windows[window_id].im_himc, &cf);
			if (windows[window_id].ime_active) {
				SetCaretPos(windows[window_id].im_position.x, windows[window_id].im_position.y);
				OS::get_singleton()->get_main_loop()->notification(MainLoop::NOTIFICATION_OS_IME_UPDATE);
			}
		} break;
		case WM_INPUTLANGCHANGEREQUEST: {
			
		} break;
		case WM_IME_STARTCOMPOSITION: {
			if (windows[window_id].ime_active) {
				windows[window_id].ime_in_progress = true;
				if (key_event_pos > 0) {
					key_event_pos--;
				}
			}
			return 0;
		} break;
		case WM_IME_ENDCOMPOSITION: {
			if (windows[window_id].ime_active) {
				windows[window_id].ime_in_progress = false;
				windows[window_id].ime_suppress_next_keyup = true;
			}
			return 0;