Fix missed test

Former-commit-id: 3b52150021ce6a3fbcdbf027c93d0320109e9d1b
Former-commit-id: 8f48ba4a2e3f37de5e4bd87ae1a176806c344791
Former-commit-id: aba9c60d1a03fff0ad4eb463143ef9a8ecd276b2

tests/ImageProcessorCore.Tests/Processors/Samplers/SamplerTests.cs

@@ -281,8 +281,10 @@
             {
                 using (FileStream stream = File.OpenRead(file))
                 {
-                    Image image = new Image(stream);
+                    
                     string filename = Path.GetFileNameWithoutExtension(file) + "-Crop" + Path.GetExtension(file);
+
+                    using (Image image = new Image(stream))
                     using (FileStream output = File.OpenWrite($"TestOutput/Crop/{filename}"))
                     {
                         image.Crop(image.Width / 2, image.Height / 2, this.ProgressUpdate).Save(output);