gui/preferences: Update Display resolution list on game window resize

This fixes the window size in the dropdown menu becoming completely
out of sync as the game window gets resized by the player with the
Display section visible.

src/gui/dialogs/preferences_dialog.cpp

@@ -415,6 +415,8 @@ void preferences_dialog::post_build(window& window)
 	connect_signal_notify_modified(res_list,
 		std::bind(&preferences_dialog::handle_res_select, this));
 
+	window.connect_signal<event::SDL_VIDEO_RESIZE>(std::bind(&preferences_dialog::set_resolution_list, this, std::ref(res_list)));
+
 	/* SHOW FLOATING LABELS */
 	register_bool("show_floating_labels", true,
 		show_floating_labels, set_show_floating_labels);