better error handling in osu_ui’s constructor

osu_paint_resources is not quite good yet, but osu_ui does its job now.
Now that we have exceptions at our disposal, maybe more and more
functions will start being void and raise exceptions on error.

include/ui/osu.h

@@ -103,7 +103,7 @@ struct osu_ui : public widget {
  *
  * Sliders are not painted. Instead, you must call #oshu::osu_paint_slider.
  */
-int osu_paint_resources(oshu::osu_ui&);
+void osu_paint_resources(oshu::osu_ui&);
 
 /**
  * Paint a slider.

lib/ui/osu.cc

@@ -140,18 +140,14 @@ static void connect_hits(oshu::osu_ui &view, oshu::hit *a, oshu::hit *b)
 
 namespace oshu {
 
-/**
- * \todo
- * Handle errors.
- */
 osu_ui::osu_ui(oshu::display *display, oshu::osu_game &game)
 : display(display), game(game)
 {
 	assert (display != nullptr);
 	oshu::osu_view(display);
-	int rc = oshu::osu_paint_resources(*this);
+	oshu::osu_paint_resources(*this);
 	if (oshu::create_cursor(display, &cursor) < 0)
-		rc = -1;
+		throw std::runtime_error("could not create cursor");
 	oshu::reset_view(display);
 	mouse = std::make_shared<osu_mouse>(display);
 	game.mouse = mouse;

lib/ui/osu_paint.cc

@@ -335,7 +335,7 @@ static int paint_connector(oshu::osu_ui &view)
  * \todo
  * Handle errors.
  */
-int oshu::osu_paint_resources(oshu::osu_ui &view)
+void oshu::osu_paint_resources(oshu::osu_ui &view)
 {
 	oshu::game_base *game = &view.game;
 	int start = SDL_GetTicks();
@@ -365,7 +365,6 @@ int oshu::osu_paint_resources(oshu::osu_ui &view)
 
 	int end = SDL_GetTicks();
 	oshu_log_debug("done generating the common textures in %.3f seconds", (end - start) / 1000.);
-	return 0;
 }
 
 void oshu::osu_free_resources(oshu::osu_ui &view)