Fixed switch for color type

src/ImageSharp/Formats/Jpeg/JpegEncoderCore.cs

@@ -131,14 +131,6 @@ namespace SixLabors.ImageSharp.Formats.Jpeg
             this.WriteStartOfScan(componentCount, componentIds);
 
             // Write the scan compressed data.
-            if (this.colorType == JpegColorType.Luminance)
-            {
-                // luminance quantization table only
-                new HuffmanScanEncoder(1, stream).EncodeGrayscale(image, ref luminanceQuantTable, cancellationToken);
-            }
-            else
-            {
-                // luminance and chrominance quantization tables.
             switch (this.colorType)
             {
                 case JpegColorType.YCbCrRatio444:
@@ -148,12 +140,14 @@ namespace SixLabors.ImageSharp.Formats.Jpeg
                     new HuffmanScanEncoder(6, stream).Encode420(image, ref luminanceQuantTable, ref chrominanceQuantTable, cancellationToken);
                     break;
                 case JpegColorType.Luminance:
-                        new HuffmanScanEncoder(1, stream).EncodeGrayscale(image, ref luminanceQuantTable, ref chrominanceQuantTable, cancellationToken);
+                    new HuffmanScanEncoder(1, stream).EncodeGrayscale(image, ref luminanceQuantTable, cancellationToken);
                     break;
                 case JpegColorType.Rgb:
                     new HuffmanScanEncoder(3, stream).EncodeRgb(image, ref luminanceQuantTable, cancellationToken);
                     break;
-                }
+                default:
+                    // all other non-supported color types are checked at the start of this method
+                    break;
             }
 
             // Write the End Of Image marker.