Fix memory leak in BitmapEncoder

Former-commit-id: 064795cce7107001df5fd8adc610b7d8d19ef7dc
Former-commit-id: d142c5bd63ad62e9307f80d42765d21d3a37e5e3
Former-commit-id: 9448861fae461c940d7fb493a44960c1f6238f13

src/ImageProcessor/Formats/Bmp/BmpEncoder.cs

@@ -51,8 +51,8 @@ namespace ImageProcessor.Formats
                 rowWidth += 4 - amount;
             }
 
-            BinaryWriter writer = new BinaryWriter(stream);
+            using (BinaryWriter writer = new BinaryWriter(stream))
-
+            {
                 BmpFileHeader fileHeader = new BmpFileHeader
                 {
                     Type = 19778, // BM
@@ -81,6 +81,7 @@ namespace ImageProcessor.Formats
 
                 writer.Flush();
             }
+        }
 
         /// <summary>
         /// Writes the pixel data to the binary stream.
@@ -100,6 +101,7 @@ namespace ImageProcessor.Formats
                 amount = 4 - amount;
             }
 
+            // TODO: Make this parallel.
             for (int y = image.Height - 1; y >= 0; y--)
             {
                 for (int x = 0; x < image.Width; x++)