added failing tests for #464

tests/ImageSharp.Tests/Formats/Jpg/JpegDecoderTests.cs

@@ -43,6 +43,7 @@ namespace SixLabors.ImageSharp.Tests.Formats.Jpg
                 TestImages.Jpeg.Baseline.Bad.BadEOF,
                 TestImages.Jpeg.Baseline.Bad.ExifUndefType,
                 TestImages.Jpeg.Issues.MultiHuffmanBaseline394,
+                TestImages.Jpeg.Issues.CmykIssueBaseline464
             };
 
         public static string[] ProgressiveTestJpegs =

tests/ImageSharp.Tests/Formats/Jpg/SpectralJpegTests.cs

@@ -29,6 +29,7 @@ namespace SixLabors.ImageSharp.Tests.Formats.Jpg
                 TestImages.Jpeg.Baseline.Jpeg444, TestImages.Jpeg.Baseline.Testorig420,
                 TestImages.Jpeg.Baseline.Jpeg420Small, TestImages.Jpeg.Baseline.Bad.BadEOF,
                 TestImages.Jpeg.Baseline.Bad.ExifUndefType,
+                TestImages.Jpeg.Issues.CmykIssueBaseline464
             };
 
         public static readonly string[] ProgressiveTestJpegs = 

tests/ImageSharp.Tests/TestImages.cs

@@ -129,6 +129,7 @@ namespace SixLabors.ImageSharp.Tests
                 public const string BadCoeffsProgressive178 = "Jpg/issues/Issue178-BadCoeffsProgressive-Lemon.jpg";
                 public const string BadZigZagProgressive385 = "Jpg/issues/Issue385-BadZigZag-Progressive.jpg";
                 public const string MultiHuffmanBaseline394 = "Jpg/issues/Issue394-MultiHuffmanBaseline-Speakers.jpg";
+                public const string CmykIssueBaseline464 = "Jpg/issues/Issue464-CMYK-DecodedAsGrayscale.jpg";
             }
 
             public static readonly string[] All = Baseline.All.Concat(Progressive.All).ToArray();

tests/Images/External

@@ -1 +1 @@
-Subproject commit 20f83891ce75597486f5532010a8c5dea1419a4d
+Subproject commit cdc178daa552856157d1834ad136f9a28996a0f9

tests/Images/Input/Jpg/issues/Issue464-CMYK-DecodedAsGrayscale.jpg

@@ -0,0 +1,3 @@
+version https://git-lfs.github.com/spec/v1
+oid sha256:96f29bee2175f34b9637d684f8336bc3e5d2bb2711cef352bc9def6ed4424d04
+size 47443