GUI2 MP lobby: fix the game list jumping to top when a new game starts

The fix is to restore the previous scroll position after the window is
laid out as a result of the new list item.

I also demoted one log message from info to debug level. It was way too
frequent for the info level.

src/gui/widgets/control.cpp

@@ -428,7 +428,7 @@ void tcontrol::definition_load_configuration(const std::string& control_type)
 	{
 		// TODO: Some widgets (toggle panel, toggle button) have a variable canvas count which is determined by its definition.
 		// I think we should remove the canvas_count from tcontrols constructor and always read it from the definition.
-		LOG_GUI_L << "Corrected canvas count to " << config()->state.size();
+		DBG_GUI_L << "Corrected canvas count to " << config()->state.size() << std::endl;
 		canvas() = std::vector<tcanvas>(config()->state.size());
 	}
 	for(size_t i = 0; i < canvas().size(); ++i) {

src/gui/widgets/listbox.cpp

@@ -35,6 +35,8 @@
 
 #include "utils/functional.hpp"
 
+#include <boost/optional.hpp>
+
 #define LOG_SCOPE_HEADER get_control_type() + " [" + id() + "] " + __func__
 #define LOG_HEADER LOG_SCOPE_HEADER + ':'
 
@@ -313,26 +315,22 @@ bool tlistbox::update_content_size()
 
 void tlistbox::place(const tpoint& origin, const tpoint& size)
 {
+	boost::optional<unsigned> vertical_scrollbar_position, horizontal_scrollbar_position;
+	// Check if this is the first time placing the list box
+	if (get_origin() != tpoint{-1, -1})
+	{
+		vertical_scrollbar_position = get_vertical_scrollbar_item_position();
+		horizontal_scrollbar_position = get_horizontal_scrollbar_item_position();
+	}
+
 	// Inherited.
 	tscrollbar_container::place(origin, size);
 
-	/**
-	 * @todo Work-around to set the selected item visible again.
-	 *
-	 * At the moment the listboxes and dialogs in general are resized a lot as
-	 * work-around for sizing. So this function makes the selected item in view
-	 * again. It doesn't work great in all cases but the proper fix is to avoid
-	 * resizing dialogs a lot. Need more work later on.
-	 */
-	const int selected_item = generator_->get_selected_item();
-	if(selected_item != -1) {
-		const SDL_Rect& visible = content_visible_area();
-		SDL_Rect rect = generator_->item(selected_item).get_rectangle();
-
-		rect.x = visible.x;
-		rect.w = visible.w;
-
-		show_content_rect(rect);
+	if (vertical_scrollbar_position && horizontal_scrollbar_position)
+	{
+		LOG_GUI_L << LOG_HEADER << " restoring scroll position" << std::endl;
+		set_vertical_scrollbar_item_position(*vertical_scrollbar_position);
+		set_horizontal_scrollbar_item_position(*horizontal_scrollbar_position);
 	}
 }
 

src/gui/widgets/scrollbar_container.cpp

@@ -1004,6 +1004,22 @@ void tscrollbar_container::set_vertical_scrollbar_item_position(
 	scrollbar_moved();
 }
 
+unsigned tscrollbar_container::get_horizontal_scrollbar_item_position() const
+{
+	assert(horizontal_scrollbar_);
+
+	return horizontal_scrollbar_->get_item_position();
+}
+
+void tscrollbar_container::set_horizontal_scrollbar_item_position(
+	const unsigned position)
+{
+	assert(horizontal_scrollbar_);
+
+	horizontal_scrollbar_->set_item_position(position);
+	scrollbar_moved();
+}
+
 void tscrollbar_container::scroll_vertical_scrollbar(
 		const tscrollbar_::tscroll scroll)
 {

src/gui/widgets/scrollbar_container.hpp

@@ -194,6 +194,19 @@ class tscrollbar_container : public tcontainer_
 	 */
 	void set_vertical_scrollbar_item_position(const unsigned position);
 
+	/**
+	 * Returns current position of the horizontal scrollbar.
+	 *
+	 */
+	unsigned get_horizontal_scrollbar_item_position() const;
+
+	/**
+	 * Move the horizontal scrollbar to a position.
+	 *
+	 * @param position              The position to scroll to.
+	 */
+	void set_horizontal_scrollbar_item_position(const unsigned position);
+
 	/**
 	 * Scrolls the vertical scrollbar.
 	 *