Fix crash on restart after update.

Also make update process more graceful.

osu.Desktop/Overlays/VersionManager.cs

@@ -189,19 +189,24 @@ protected override void PopOut()
 
         private class UpdateProgressNotification : ProgressNotification
         {
+            private OsuGame game;
+
             protected override Notification CreateCompletionNotification() => new ProgressCompletionNotification()
             {
                 Text = @"Update ready to install. Click to restart!",
                 Activated = () =>
                 {
-                    UpdateManager.RestartApp();
+                    UpdateManager.RestartAppWhenExited();
+                    game.GracefullyExit();
                     return true;
                 }
             };
 
             [BackgroundDependencyLoader]
-            private void load(OsuColour colours)
+            private void load(OsuColour colours, OsuGame game)
             {
+                this.game = game;
+
                 IconContent.Add(new Drawable[]
                 {
                     new Box

osu.Game/OsuGame.cs

@@ -307,6 +307,18 @@ protected override bool OnExiting()
             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();