fix: failed to discard changes in a new file which has been staged partically (#2189)

Signed-off-by: leo <longshuang@msn.cn>

Author: love-linger

src/Models/DiffResult.cs

@@ -124,9 +124,9 @@ public void GenerateNewPatchFromSelection(Change change, string fileBlobGuid, Te
                         continue;
 
                     if (i >= selection.StartLine - 1 && i < selection.EndLine)
-                        writer.WriteLine($"+{line.Content}");
+                        WriteLine(writer, '+', line);
                     else
-                        writer.WriteLine($" {line.Content}");
+                        WriteLine(writer, ' ', line);
                 }
             }
             else
@@ -137,11 +137,10 @@ public void GenerateNewPatchFromSelection(Change change, string fileBlobGuid, Te
                     var line = Lines[i];
                     if (line.Type != TextDiffLineType.Added)
                         continue;
-                    writer.WriteLine($"+{line.Content}");
+                    WriteLine(writer, '+', line);
                 }
             }
 
-            writer.WriteLine("\\ No newline at end of file");
             writer.Flush();
         }
 

src/Views/TextDiffView.axaml.cs

@@ -1562,7 +1562,7 @@ private async void OnDiscardChunk(object _1, RoutedEventArgs _2)
             using var lockWatcher = repo.LockWatcher();
 
             var tmpFile = Path.GetTempFileName();
-            if (change.Index == Models.ChangeState.Added)
+            if (change.WorkTree == Models.ChangeState.Untracked)
             {
                 diff.GenerateNewPatchFromSelection(change, null, selection, true, tmpFile);
             }