fix: crash when create image from a empty stream

Author: love-linger

src/Commands/QueryFileContent.cs

@@ -17,23 +17,23 @@ public static Stream Run(string repo, string revision, string file)
             starter.WindowStyle = ProcessWindowStyle.Hidden;
             starter.RedirectStandardOutput = true;
 
+            var stream = new MemoryStream();
             try
             {
-                var stream = new MemoryStream();
                 var proc = new Process() { StartInfo = starter };
                 proc.Start();
                 proc.StandardOutput.BaseStream.CopyTo(stream);
                 proc.WaitForExit();
                 proc.Close();
 
                 stream.Position = 0;
-                return stream;
             }
             catch (Exception e)
             {
                 App.RaiseException(repo, $"Failed to query file content: {e}");
-                return null;
             }
+
+            return stream;
         }
     }
 }

src/ViewModels/CommitDetail.cs

@@ -475,7 +475,7 @@ private void RefreshViewRevisionFile(Models.Object file)
                             if (IMG_EXTS.Contains(ext))
                             {
                                 var stream = Commands.QueryFileContent.Run(_repo, _commit.SHA, file.Path);
-                                var bitmap = stream != null ? new Bitmap(stream) : null as Bitmap;
+                                var bitmap = stream.Length > 0 ? new Bitmap(stream) : null;
                                 Dispatcher.UIThread.Invoke(() =>
                                 {
                                     ViewRevisionFileContent = new Models.RevisionImageFile() { Image = bitmap };

src/ViewModels/DiffContext.cs

@@ -166,7 +166,7 @@ public void OpenExternalMergeTool()
         private Bitmap BitmapFromRevisionFile(string repo, string revision, string file)
         {
             var stream = Commands.QueryFileContent.Run(repo, revision, file);
-            return stream != null ? new Bitmap(stream) : null;
+            return stream.Length > 0 ? new Bitmap(stream) : null;
         }
 
         private static readonly HashSet<string> IMG_EXTS = new HashSet<string>()