### 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)

_send_window_event(windows[window_mouseover_id], WINDOW_EVENT_MOUSE_EXIT);
					}
					_send_window_event(windows[window_id], WINDOW_EVENT_MOUSE_ENTER);
				}
				CursorShape c = cursor_shape;
				cursor_shape = CURSOR_MAX;
				cursor_set_shape(c);
				window_mouseover_id = window_id;
				
				track_mouse_leave_event(hWnd);
			}
			
			if (!windows[window_id].window_has_focus && mouse_mode == MOUSE_MODE_CAPTURED) {
				break;
			}
			Ref<InputEventMouseMotion> mm;
			mm.instantiate();
			mm->set_window_id(window_id);
			if (pen_info.penMask & PEN_MASK_PRESSURE) {
				mm->set_pressure((float)pen_info.pressure / 1024);
			} else {
				mm->set_pressure((HIWORD(wParam) & POINTER_MESSAGE_FLAG_FIRSTBUTTON) ? 1.0f : 0.0f);
			}
			if ((pen_info.penMask & PEN_MASK_TILT_X) && (pen_info.penMask & PEN_MASK_TILT_Y)) {
				mm->set_tilt(Vector2((float)pen_info.tiltX / 90, (float)pen_info.tiltY / 90));
			}
			mm->set_pen_inverted(pen_info.penFlags & (PEN_FLAG_INVERTED | PEN_FLAG_ERASER));
			mm->set_ctrl_pressed(GetKeyState(VK_CONTROL) < 0);
			mm->set_shift_pressed(GetKeyState(VK_SHIFT) < 0);