Fix crash on restart after update.

Also make update process more graceful.

osu.Game/OsuGame.cs

@@ -307,6 +307,18 @@ namespace osu.Game
             return base.OnExiting();
         }
 
+        /// <summary>
+        /// Use to programatically exit the game as if the user was triggering via alt-f4.
+        /// Will keep persisting until an exit occurs (exit may be blocked multiple times).
+        /// </summary>
+        public void GracefullyExit()
+        {
+            if (!OnExiting())
+                Exit();
+            else
+                Scheduler.AddDelayed(GracefullyExit, 2000);
+        }
+
         protected override void UpdateAfterChildren()
         {
             base.UpdateAfterChildren();