Merge pull request #10730 from peppy/fix-patcher-no-object-crash

Fix legacy patcher crash on no objects present

osu.Game.Tests/Editing/LegacyEditorBeatmapPatcherTest.cs

@@ -37,6 +37,12 @@ namespace osu.Game.Tests.Editing
             }));
         }
 
+        [Test]
+        public void TestPatchNoObjectChanges()
+        {
+            runTest(new OsuBeatmap());
+        }
+
         [Test]
         public void TestAddHitObject()
         {

osu.Game/Beatmaps/Formats/LegacyBeatmapEncoder.cs

@@ -235,11 +235,11 @@ namespace osu.Game.Beatmaps.Formats
 
         private void handleHitObjects(TextWriter writer)
         {
+            writer.WriteLine("[HitObjects]");
+
             if (beatmap.HitObjects.Count == 0)
                 return;
 
-            writer.WriteLine("[HitObjects]");
-
             foreach (var h in beatmap.HitObjects)
                 handleHitObject(writer, h);
         }

osu.Game/Screens/Edit/LegacyEditorBeatmapPatcher.cs

@@ -3,6 +3,7 @@
 
 using System;
 using System.Collections.Generic;
+using System.Diagnostics;
 using System.IO;
 using System.Text;
 using DiffPlex;
@@ -35,6 +36,9 @@ namespace osu.Game.Screens.Edit
             int oldHitObjectsIndex = Array.IndexOf(result.PiecesOld, "[HitObjects]");
             int newHitObjectsIndex = Array.IndexOf(result.PiecesNew, "[HitObjects]");
 
+            Debug.Assert(oldHitObjectsIndex >= 0);
+            Debug.Assert(newHitObjectsIndex >= 0);
+
             var toRemove = new List<int>();
             var toAdd = new List<int>();