Codechange: Pass WindowDesc by reference instead of pointer. (#12771)

WindowDesc as passed to Windows is not optional so don't allow to it to be nullptr.

src/ai/ai_gui.cpp

@@ -97,7 +97,7 @@ struct AIConfigWindow : public Window {
 	int line_height;         ///< Height of a single AI-name line.
 	Scrollbar *vscroll;      ///< Cache of the vertical scrollbar.
 
-	AIConfigWindow() : Window(&_ai_config_desc)
+	AIConfigWindow() : Window(_ai_config_desc)
 	{
 		this->InitNested(WN_GAME_OPTIONS_AI); // Initializes 'this->line_height' as a side effect.
 		this->vscroll = this->GetScrollbar(WID_AIC_SCROLLBAR);