Skip SOS contents when parsing metadata only

src/ImageSharp/Formats/Jpeg/GolangPort/OrigJpegDecoderCore.cs

@@ -361,16 +361,19 @@ namespace SixLabors.ImageSharp.Formats.Jpeg.GolangPort
 
                         break;
                     case OrigJpegConstants.Markers.SOS:
-                        if (!metadataOnly)
+                        if (metadataOnly)
                         {
-                            this.ProcessStartOfScanMarker(remaining);
+                            this.InputProcessor.Skip(remaining);
                         }
-
+                        else
+                        {
+                            this.ProcessStartOfScanMarker(remaining);
                             if (this.InputProcessor.ReachedEOF)
                             {
                                 // If unexpected EOF reached. We can stop processing bytes as we now have the image data.
                                 processBytes = false;
                             }
+                        }
 
                         break;
                     case OrigJpegConstants.Markers.DRI:

src/ImageSharp/Formats/Jpeg/PdfJsPort/PdfJsJpegDecoderCore.cs

@@ -246,7 +246,11 @@ namespace SixLabors.ImageSharp.Formats.Jpeg.PdfJsPort
                             break;
 
                         case PdfJsJpegConstants.Markers.SOS:
-                            if (!metadataOnly)
+                            if (metadataOnly)
+                            {
+                                this.InputStream.Skip(remaining);
+                            }
+                            else
                             {
                                 this.ProcessStartOfScanMarker();
                             }